(backport only)

We're about to grow the exception handlers, which will make a bunch of them no longer fit within the space available. We move them out of line.

This is a fiddly and error-prone business, so in the interests of reviewability I haven't merged this in with the addition of the entry flush.

Signed-off-by: Daniel Axtens dja@axtens.net --- arch/powerpc/kernel/exceptions-64s.S | 138 +++++++++++++++++---------- 1 file changed, 90 insertions(+), 48 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 536718ed033f..3d843e1a162c 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -202,8 +202,8 @@ ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE) data_access_pSeries: HMT_MEDIUM_PPR_DISCARD SET_SCRATCH0(r13) - EXCEPTION_PROLOG_PSERIES(PACA_EXGEN, data_access_common, EXC_STD, - KVMTEST, 0x300) + EXCEPTION_PROLOG_0(PACA_EXGEN) + b data_access_pSeries_ool

. = 0x380 .globl data_access_slb_pSeries @@ -211,31 +211,15 @@ data_access_slb_pSeries: HMT_MEDIUM_PPR_DISCARD SET_SCRATCH0(r13) EXCEPTION_PROLOG_0(PACA_EXSLB) - EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST, 0x380) - std r3,PACA_EXSLB+EX_R3(r13) - mfspr r3,SPRN_DAR -#ifdef __DISABLED__ - /* Keep that around for when we re-implement dynamic VSIDs */ - cmpdi r3,0 - bge slb_miss_user_pseries -#endif /* __DISABLED__ */ - mfspr r12,SPRN_SRR1 -#ifndef CONFIG_RELOCATABLE - b slb_miss_realmode -#else - /* - * We can't just use a direct branch to slb_miss_realmode - * because the distance from here to there depends on where - * the kernel ends up being put. - */ - mfctr r11 - ld r10,PACAKBASE(r13) - LOAD_HANDLER(r10, slb_miss_realmode) - mtctr r10 - bctr -#endif + b data_access_slb_pSeries_ool

- STD_EXCEPTION_PSERIES(0x400, 0x400, instruction_access) + . = 0x400 + .globl instruction_access_pSeries +instruction_access_pSeries: + HMT_MEDIUM_PPR_DISCARD + SET_SCRATCH0(r13) + EXCEPTION_PROLOG_0(PACA_EXGEN) + b instruction_access_pSeries_ool

. = 0x480 .globl instruction_access_slb_pSeries @@ -243,24 +227,7 @@ instruction_access_slb_pSeries: HMT_MEDIUM_PPR_DISCARD SET_SCRATCH0(r13) EXCEPTION_PROLOG_0(PACA_EXSLB) - EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST_PR, 0x480) - std r3,PACA_EXSLB+EX_R3(r13) - mfspr r3,SPRN_SRR0 /* SRR0 is faulting address */ -#ifdef __DISABLED__ - /* Keep that around for when we re-implement dynamic VSIDs */ - cmpdi r3,0 - bge slb_miss_user_pseries -#endif /* __DISABLED__ */ - mfspr r12,SPRN_SRR1 -#ifndef CONFIG_RELOCATABLE - b slb_miss_realmode -#else - mfctr r11 - ld r10,PACAKBASE(r13) - LOAD_HANDLER(r10, slb_miss_realmode) - mtctr r10 - bctr -#endif + b instruction_access_slb_pSeries_ool

/* We open code these as we can't have a ". = x" (even with * x = "." within a feature section @@ -291,13 +258,19 @@ hardware_interrupt_hv: KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0x800)

. = 0x900 - .globl decrementer_pSeries -decrementer_pSeries: + .globl decrementer_trampoline +decrementer_trampoline: SET_SCRATCH0(r13) EXCEPTION_PROLOG_0(PACA_EXGEN) b decrementer_ool

- STD_EXCEPTION_HV(0x980, 0x982, hdecrementer) + . = 0x980 + .globl hdecrementer_trampoline +hdecrementer_trampoline: + HMT_MEDIUM_PPR_DISCARD; + SET_SCRATCH0(r13); + EXCEPTION_PROLOG_0(PACA_EXGEN) + b hdecrementer_hv

MASKABLE_EXCEPTION_PSERIES(0xa00, 0xa00, doorbell_super) KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0xa00) @@ -545,6 +518,64 @@ machine_check_pSeries_0: KVM_HANDLER_PR(PACA_EXGEN, EXC_STD, 0x900) KVM_HANDLER(PACA_EXGEN, EXC_HV, 0x982)

+/* moved from 0x300 */ + .globl data_access_pSeries_ool +data_access_pSeries_ool: + EXCEPTION_PROLOG_1(PACA_EXGEN, KVMTEST, 0x300) + EXCEPTION_PROLOG_PSERIES_1(data_access_common, EXC_STD) + + .globl data_access_slb_pSeries_ool +data_access_slb_pSeries_ool: + EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST, 0x380) + std r3,PACA_EXSLB+EX_R3(r13) + mfspr r3,SPRN_DAR +#ifdef __DISABLED__ + /* Keep that around for when we re-implement dynamic VSIDs */ + cmpdi r3,0 + bge slb_miss_user_pseries +#endif /* __DISABLED__ */ + mfspr r12,SPRN_SRR1 +#ifndef CONFIG_RELOCATABLE + b slb_miss_realmode +#else + /* + * We can't just use a direct branch to slb_miss_realmode + * because the distance from here to there depends on where + * the kernel ends up being put. + */ + mfctr r11 + ld r10,PACAKBASE(r13) + LOAD_HANDLER(r10, slb_miss_realmode) + mtctr r10 + bctr +#endif + + .globl instruction_access_pSeries_ool +instruction_access_pSeries_ool: + EXCEPTION_PROLOG_1(PACA_EXGEN, KVMTEST_PR, 0x400) + EXCEPTION_PROLOG_PSERIES_1(instruction_access_common, EXC_STD) + + .globl instruction_access_slb_pSeries_ool +instruction_access_slb_pSeries_ool: + EXCEPTION_PROLOG_1(PACA_EXSLB, KVMTEST_PR, 0x480) + std r3,PACA_EXSLB+EX_R3(r13) + mfspr r3,SPRN_SRR0 /* SRR0 is faulting address */ +#ifdef __DISABLED__ + /* Keep that around for when we re-implement dynamic VSIDs */ + cmpdi r3,0 + bge slb_miss_user_pseries +#endif /* __DISABLED__ */ + mfspr r12,SPRN_SRR1 +#ifndef CONFIG_RELOCATABLE + b slb_miss_realmode +#else + mfctr r11 + ld r10,PACAKBASE(r13) + LOAD_HANDLER(r10, slb_miss_realmode) + mtctr r10 + bctr +#endif + #ifdef CONFIG_PPC_DENORMALISATION denorm_assist: BEGIN_FTR_SECTION @@ -612,6 +643,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR) .align 7 /* moved from 0xe00 */ MASKABLE_EXCEPTION_OOL(0x900, decrementer) + STD_EXCEPTION_HV_OOL(0x982, hdecrementer) STD_EXCEPTION_HV_OOL(0xe02, h_data_storage) KVM_HANDLER_SKIP(PACA_EXGEN, EXC_HV, 0xe02) STD_EXCEPTION_HV_OOL(0xe22, h_instr_storage) @@ -894,7 +926,15 @@ hardware_interrupt_relon_hv: STD_RELON_EXCEPTION_PSERIES(0x4600, 0x600, alignment) STD_RELON_EXCEPTION_PSERIES(0x4700, 0x700, program_check) STD_RELON_EXCEPTION_PSERIES(0x4800, 0x800, fp_unavailable) - MASKABLE_RELON_EXCEPTION_PSERIES(0x4900, 0x900, decrementer) + + . = 0x4900 + .globl decrementer_relon_trampoline +decrementer_relon_trampoline: + HMT_MEDIUM_PPR_DISCARD + SET_SCRATCH0(r13) + EXCEPTION_PROLOG_0(PACA_EXGEN) + b decrementer_relon_pSeries + STD_RELON_EXCEPTION_HV(0x4980, 0x982, hdecrementer) MASKABLE_RELON_EXCEPTION_PSERIES(0x4a00, 0xa00, doorbell_super) STD_RELON_EXCEPTION_PSERIES(0x4b00, 0xb00, trap_0b) @@ -1244,6 +1284,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX) __end_handlers:

/* Equivalents to the above handlers for relocation-on interrupt vectors */ + MASKABLE_RELON_EXCEPTION_PSERIES_OOL(0x900, decrementer) + STD_RELON_EXCEPTION_HV_OOL(0xe40, emulation_assist) MASKABLE_RELON_EXCEPTION_HV_OOL(0xe80, h_doorbell)

From: Christophe Leroy christophe.leroy@c-s.fr

Backported from commit de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection"). Here we don't try to add the KUAP framework, we just want the helper functions because we want to put uaccess flush helpers in them.

In terms of fixes, we don't need commit 1d8f739b07bd ("powerpc/kuap: Fix set direction in allow/prevent_user_access()") as we don't have real KUAP. Likewise as all our allows are noops and all our prevents are just flushes, we don't need commit 9dc086f1e9ef ("powerpc/futex: Fix incorrect user access blocking") The other 2 fixes we do need.

The original description is:

This patch implements a framework for Kernel Userspace Access Protection.

Then subarches will have the possibility to provide their own implementation by providing setup_kuap() and allow/prevent_user_access().

Some platforms will need to know the area accessed and whether it is accessed from read, write or both. Therefore source, destination and size and handed over to the two functions.

mpe: Rename to allow/prevent rather than unlock/lock, and add read/write wrappers. Drop the 32-bit code for now until we have an implementation for it. Add kuap to pt_regs for 64-bit as well as 32-bit. Don't split strings, use pr_crit_ratelimited().

Signed-off-by: Christophe Leroy christophe.leroy@c-s.fr Signed-off-by: Russell Currey ruscur@russell.cc Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Daniel Axtens dja@axtens.net --- arch/powerpc/include/asm/futex.h | 4 +++ arch/powerpc/include/asm/kup.h | 36 +++++++++++++++++++++++ arch/powerpc/include/asm/uaccess.h | 38 +++++++++++++++++++------ arch/powerpc/lib/checksum_wrappers_64.c | 4 +++ 4 files changed, 74 insertions(+), 8 deletions(-) create mode 100644 arch/powerpc/include/asm/kup.h

diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h index b73ab8a7ebc3..10746519b351 100644 --- a/arch/powerpc/include/asm/futex.h +++ b/arch/powerpc/include/asm/futex.h @@ -36,6 +36,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, { int oldval = 0, ret;

+ allow_write_to_user(uaddr, sizeof(*uaddr)); pagefault_disable();

switch (op) { @@ -62,6 +63,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,

*oval = oldval;

+ prevent_write_to_user(uaddr, sizeof(*uaddr)); return ret; }

@@ -75,6 +77,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32))) return -EFAULT;

+ allow_write_to_user(uaddr, sizeof(*uaddr)); __asm__ __volatile__ ( PPC_ATOMIC_ENTRY_BARRIER "1: lwarx %1,0,%3 # futex_atomic_cmpxchg_inatomic\n\ @@ -97,6 +100,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr, : "cc", "memory");

*uval = prev; + prevent_write_to_user(uaddr, sizeof(*uaddr)); return ret; }

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h new file mode 100644 index 000000000000..7895d5eeaf21 --- /dev/null +++ b/arch/powerpc/include/asm/kup.h @@ -0,0 +1,36 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_POWERPC_KUP_H_ +#define _ASM_POWERPC_KUP_H_ + +#ifndef __ASSEMBLY__ + +#include <asm/pgtable.h> + +static inline void allow_user_access(void __user *to, const void __user *from, + unsigned long size) { } +static inline void prevent_user_access(void __user *to, const void __user *from, + unsigned long size) { } + +static inline void allow_read_from_user(const void __user *from, unsigned long size) +{ + allow_user_access(NULL, from, size); +} + +static inline void allow_write_to_user(void __user *to, unsigned long size) +{ + allow_user_access(to, NULL, size); +} + +static inline void prevent_read_from_user(const void __user *from, unsigned long size) +{ + prevent_user_access(NULL, from, size); +} + +static inline void prevent_write_to_user(void __user *to, unsigned long size) +{ + prevent_user_access(to, NULL, size); +} + +#endif /* !__ASSEMBLY__ */ + +#endif /* _ASM_POWERPC_KUP_H_ */ diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index e51ce5a0e221..50d3c953b33e 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -9,6 +9,7 @@ #include <asm/asm-compat.h> #include <asm/processor.h> #include <asm/page.h> +#include <asm/kup.h>

#define VERIFY_READ 0 #define VERIFY_WRITE 1 @@ -164,6 +165,7 @@ extern long __put_user_bad(void); #define __put_user_size(x, ptr, size, retval) \ do { \ retval = 0; \ + allow_write_to_user(ptr, size); \ switch (size) { \ case 1: __put_user_asm(x, ptr, retval, "stb"); break; \ case 2: __put_user_asm(x, ptr, retval, "sth"); break; \ @@ -171,6 +173,7 @@ do { \ case 8: __put_user_asm2(x, ptr, retval); break; \ default: __put_user_bad(); \ } \ + prevent_write_to_user(ptr, size); \ } while (0)

#define __put_user_nocheck(x, ptr, size) \ @@ -252,6 +255,7 @@ do { \ __chk_user_ptr(ptr); \ if (size > sizeof(x)) \ (x) = __get_user_bad(); \ + allow_read_from_user(ptr, size); \ switch (size) { \ case 1: __get_user_asm(x, ptr, retval, "lbz"); break; \ case 2: __get_user_asm(x, ptr, retval, "lhz"); break; \ @@ -259,6 +263,7 @@ do { \ case 8: __get_user_asm2(x, ptr, retval); break; \ default: (x) = __get_user_bad(); \ } \ + prevent_read_from_user(ptr, size); \ } while (0)

#define __get_user_nocheck(x, ptr, size) \ @@ -328,9 +333,14 @@ extern unsigned long __copy_tofrom_user(void __user *to, static inline unsigned long copy_from_user(void *to, const void __user *from, unsigned long n) { + unsigned long ret; + if (likely(access_ok(VERIFY_READ, from, n))) { + allow_user_access(to, from, n); barrier_nospec(); - return __copy_tofrom_user((__force void __user *)to, from, n); + ret = __copy_tofrom_user((__force void __user *)to, from, n); + prevent_user_access(to, from, n); + return ret; } memset(to, 0, n); return n; @@ -361,8 +371,9 @@ extern unsigned long copy_in_user(void __user *to, const void __user *from, static inline unsigned long __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n) { + unsigned long ret; if (__builtin_constant_p(n) && (n <= 8)) { - unsigned long ret = 1; + ret = 1;

switch (n) { case 1: @@ -387,14 +398,18 @@ static inline unsigned long __copy_from_user_inatomic(void *to, }

barrier_nospec(); - return __copy_tofrom_user((__force void __user *)to, from, n); + allow_read_from_user(from, n); + ret = __copy_tofrom_user((__force void __user *)to, from, n); + prevent_read_from_user(from, n); + return ret; }

static inline unsigned long __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n) { + unsigned long ret; if (__builtin_constant_p(n) && (n <= 8)) { - unsigned long ret = 1; + ret = 1;

switch (n) { case 1: @@ -414,7 +429,10 @@ static inline unsigned long __copy_to_user_inatomic(void __user *to, return 0; }

- return __copy_tofrom_user(to, (__force const void __user *)from, n); + allow_write_to_user(to, n); + ret = __copy_tofrom_user(to, (__force const void __user *)from, n); + prevent_write_to_user(to, n); + return ret; }

static inline unsigned long __copy_from_user(void *to, @@ -435,10 +453,14 @@ extern unsigned long __clear_user(void __user *addr, unsigned long size);

static inline unsigned long clear_user(void __user *addr, unsigned long size) { + unsigned long ret = size; might_fault(); - if (likely(access_ok(VERIFY_WRITE, addr, size))) - return __clear_user(addr, size); - return size; + if (likely(access_ok(VERIFY_WRITE, addr, size))) { + allow_write_to_user(addr, size); + ret = __clear_user(addr, size); + prevent_write_to_user(addr, size); + } + return ret; }

extern long strncpy_from_user(char *dst, const char __user *src, long count); diff --git a/arch/powerpc/lib/checksum_wrappers_64.c b/arch/powerpc/lib/checksum_wrappers_64.c index 08e3a3356c40..11b58949eb62 100644 --- a/arch/powerpc/lib/checksum_wrappers_64.c +++ b/arch/powerpc/lib/checksum_wrappers_64.c @@ -29,6 +29,7 @@ __wsum csum_and_copy_from_user(const void __user *src, void *dst, unsigned int csum;

might_sleep(); + allow_read_from_user(src, len);

*err_ptr = 0;

@@ -60,6 +61,7 @@ __wsum csum_and_copy_from_user(const void __user *src, void *dst, }

out: + prevent_read_from_user(src, len); return (__force __wsum)csum; } EXPORT_SYMBOL(csum_and_copy_from_user); @@ -70,6 +72,7 @@ __wsum csum_and_copy_to_user(const void *src, void __user *dst, int len, unsigned int csum;

might_sleep(); + allow_write_to_user(dst, len);

*err_ptr = 0;

@@ -97,6 +100,7 @@ __wsum csum_and_copy_to_user(const void *src, void __user *dst, int len, }

out: + prevent_write_to_user(dst, len); return (__force __wsum)csum; } EXPORT_SYMBOL(csum_and_copy_to_user);

From: Andrew Donnellan ajd@linux.ibm.com

commit 61e3acd8c693a14fc69b824cb5b08d02cb90a6e7 upstream.

The KUAP implementation adds calls in clear_user() to enable and disable access to userspace memory. However, it doesn't add these to __clear_user(), which is used in the ptrace regset code.

As there's only one direct user of __clear_user() (the regset code), and the time taken to set the AMR for KUAP purposes is going to dominate the cost of a quick access_ok(), there's not much point having a separate path.

Rename __clear_user() to __arch_clear_user(), and make __clear_user() just call clear_user().

Reported-by: syzbot+f25ecf4b2982d8c7a640@syzkaller-ppc64.appspotmail.com Reported-by: Daniel Axtens dja@axtens.net Suggested-by: Michael Ellerman mpe@ellerman.id.au Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection") Signed-off-by: Andrew Donnellan ajd@linux.ibm.com [mpe: Use __arch_clear_user() for the asm version like arm64 & nds32] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20191209132221.15328-1-ajd@linux.ibm.com Signed-off-by: Daniel Axtens dja@axtens.net --- arch/powerpc/include/asm/uaccess.h | 9 +++++++-- arch/powerpc/kernel/ppc_ksyms.c | 3 +++ arch/powerpc/lib/string.S | 2 +- arch/powerpc/lib/string_64.S | 4 ++-- 4 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h index f0195ad25836..edf211b5ada0 100644 --- a/arch/powerpc/include/asm/uaccess.h +++ b/arch/powerpc/include/asm/uaccess.h @@ -471,7 +471,7 @@ static inline unsigned long __copy_to_user(void __user *to, return __copy_to_user_inatomic(to, from, size); }

-extern unsigned long __clear_user(void __user *addr, unsigned long size); +unsigned long __arch_clear_user(void __user *addr, unsigned long size);

static inline unsigned long clear_user(void __user *addr, unsigned long size) { @@ -479,12 +479,17 @@ static inline unsigned long clear_user(void __user *addr, unsigned long size) might_fault(); if (likely(access_ok(VERIFY_WRITE, addr, size))) { allow_write_to_user(addr, size); - ret = __clear_user(addr, size); + ret = __arch_clear_user(addr, size); prevent_write_to_user(addr, size); } return ret; }

+static inline unsigned long __clear_user(void __user *addr, unsigned long size) +{ + return clear_user(addr, size); +} + extern long strncpy_from_user(char *dst, const char __user *src, long count); extern __must_check long strlen_user(const char __user *str); extern __must_check long strnlen_user(const char __user *str, long n); diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c index 202963ee013a..b92debacb821 100644 --- a/arch/powerpc/kernel/ppc_ksyms.c +++ b/arch/powerpc/kernel/ppc_ksyms.c @@ -5,6 +5,7 @@ #include <asm/switch_to.h> #include <asm/cacheflush.h> #include <asm/epapr_hcalls.h> +#include <asm/uaccess.h>

EXPORT_SYMBOL(flush_dcache_range); EXPORT_SYMBOL(flush_icache_range); @@ -43,3 +44,5 @@ EXPORT_SYMBOL(epapr_hypercall_start); #endif

EXPORT_SYMBOL(current_stack_pointer); + +EXPORT_SYMBOL(__arch_clear_user); diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S index c80fb49ce607..93c4c34ad091 100644 --- a/arch/powerpc/lib/string.S +++ b/arch/powerpc/lib/string.S @@ -122,7 +122,7 @@ _GLOBAL(memchr) blr

#ifdef CONFIG_PPC32 -_GLOBAL(__clear_user) +_GLOBAL(__arch_clear_user) addi r6,r3,-4 li r3,0 li r5,0 diff --git a/arch/powerpc/lib/string_64.S b/arch/powerpc/lib/string_64.S index 7bd9549a90a2..14d26ad2cd69 100644 --- a/arch/powerpc/lib/string_64.S +++ b/arch/powerpc/lib/string_64.S @@ -27,7 +27,7 @@ PPC64_CACHES: .section ".text"

/** - * __clear_user: - Zero a block of memory in user space, with less checking. + * __arch_clear_user: - Zero a block of memory in user space, with less checking. * @to: Destination address, in user space. * @n: Number of bytes to zero. * @@ -77,7 +77,7 @@ err3; stb r0,0(r3) mr r3,r4 blr

-_GLOBAL_TOC(__clear_user) +_GLOBAL_TOC(__arch_clear_user) cmpdi r4,32 neg r6,r3 li r0,0

From: Nicholas Piggin npiggin@gmail.com

commit 9a32a7e78bd0cd9a9b6332cbdc345ee5ffd0c5de upstream.

IBM Power9 processors can speculatively operate on data in the L1 cache before it has been completely validated, via a way-prediction mechanism. It is not possible for an attacker to determine the contents of impermissible memory using this method, since these systems implement a combination of hardware and software security measures to prevent scenarios where protected data could be leaked.

However these measures don't address the scenario where an attacker induces the operating system to speculatively execute instructions using data that the attacker controls. This can be used for example to speculatively bypass "kernel user access prevention" techniques, as discovered by Anthony Steinhauser of Google's Safeside Project. This is not an attack by itself, but there is a possibility it could be used in conjunction with side-channels or other weaknesses in the privileged code to construct an attack.

This issue can be mitigated by flushing the L1 cache between privilege boundaries of concern. This patch flushes the L1 cache after user accesses.

This is part of the fix for CVE-2020-4788.

Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Daniel Axtens dja@axtens.net --- Documentation/kernel-parameters.txt | 4 + .../powerpc/include/asm/book3s/64/kup-radix.h | 23 +++++ arch/powerpc/include/asm/feature-fixups.h | 9 ++ arch/powerpc/include/asm/kup.h | 4 + arch/powerpc/include/asm/security_features.h | 3 + arch/powerpc/include/asm/setup.h | 1 + arch/powerpc/kernel/exceptions-64s.S | 86 ++++++------------- arch/powerpc/kernel/ppc_ksyms.c | 7 ++ arch/powerpc/kernel/setup_64.c | 80 +++++++++++++++++ arch/powerpc/kernel/vmlinux.lds.S | 7 ++ arch/powerpc/lib/feature-fixups.c | 50 +++++++++++ arch/powerpc/platforms/powernv/setup.c | 7 +- arch/powerpc/platforms/pseries/setup.c | 4 + 13 files changed, 224 insertions(+), 61 deletions(-) create mode 100644 arch/powerpc/include/asm/book3s/64/kup-radix.h

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 007f12c79365..2c579b53d582 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2197,6 +2197,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. mds=off [X86] tsx_async_abort=off [X86] no_entry_flush [PPC] + no_uaccess_flush [PPC]

auto (default) Mitigate all CPU vulnerabilities, but leave SMT @@ -2521,6 +2522,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted. nospec_store_bypass_disable [HW] Disable all mitigations for the Speculative Store Bypass vulnerability

+ no_uaccess_flush + [PPC] Don't flush the L1-D cache after accessing user data. + noxsave [BUGS=X86] Disables x86 extended register state save and restore using xsave. The kernel will fallback to enabling legacy floating-point and sse state. diff --git a/arch/powerpc/include/asm/book3s/64/kup-radix.h b/arch/powerpc/include/asm/book3s/64/kup-radix.h new file mode 100644 index 000000000000..cce8e7497d72 --- /dev/null +++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h @@ -0,0 +1,23 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_POWERPC_BOOK3S_64_KUP_RADIX_H +#define _ASM_POWERPC_BOOK3S_64_KUP_RADIX_H +#include <linux/jump_label.h> + +DECLARE_STATIC_KEY_FALSE(uaccess_flush_key); + +/* Prototype for function defined in exceptions-64s.S */ +void do_uaccess_flush(void); + +static __always_inline void allow_user_access(void __user *to, const void __user *from, + unsigned long size) +{ +} + +static inline void prevent_user_access(void __user *to, const void __user *from, + unsigned long size) +{ + if (static_branch_unlikely(&uaccess_flush_key)) + do_uaccess_flush(); +} + +#endif /* _ASM_POWERPC_BOOK3S_64_KUP_RADIX_H */ diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h index a963c26b2d34..83219710e904 100644 --- a/arch/powerpc/include/asm/feature-fixups.h +++ b/arch/powerpc/include/asm/feature-fixups.h @@ -200,6 +200,14 @@ label##3: \ FTR_ENTRY_OFFSET 955b-956b; \ .popsection;

+#define UACCESS_FLUSH_FIXUP_SECTION \ +959: \ + .pushsection __uaccess_flush_fixup,"a"; \ + .align 2; \ +960: \ + FTR_ENTRY_OFFSET 959b-960b; \ + .popsection; + #define ENTRY_FLUSH_FIXUP_SECTION \ 957: \ .pushsection __entry_flush_fixup,"a"; \ @@ -242,6 +250,7 @@ extern long stf_barrier_fallback; extern long entry_flush_fallback; extern long __start___stf_entry_barrier_fixup, __stop___stf_entry_barrier_fixup; extern long __start___stf_exit_barrier_fixup, __stop___stf_exit_barrier_fixup; +extern long __start___uaccess_flush_fixup, __stop___uaccess_flush_fixup; extern long __start___entry_flush_fixup, __stop___entry_flush_fixup; extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup; extern long __start___barrier_nospec_fixup, __stop___barrier_nospec_fixup; diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h index 7895d5eeaf21..f0f8e36ad71f 100644 --- a/arch/powerpc/include/asm/kup.h +++ b/arch/powerpc/include/asm/kup.h @@ -6,10 +6,14 @@

#include <asm/pgtable.h>

+#ifdef CONFIG_PPC_BOOK3S_64 +#include <asm/book3s/64/kup-radix.h> +#else static inline void allow_user_access(void __user *to, const void __user *from, unsigned long size) { } static inline void prevent_user_access(void __user *to, const void __user *from, unsigned long size) { } +#endif /* CONFIG_PPC_BOOK3S_64 */

static inline void allow_read_from_user(const void __user *from, unsigned long size) { diff --git a/arch/powerpc/include/asm/security_features.h b/arch/powerpc/include/asm/security_features.h index 082b56bf678d..3b45a64e491e 100644 --- a/arch/powerpc/include/asm/security_features.h +++ b/arch/powerpc/include/asm/security_features.h @@ -87,6 +87,8 @@ static inline bool security_ftr_enabled(unsigned long feature) // The L1-D cache should be flushed when entering the kernel #define SEC_FTR_L1D_FLUSH_ENTRY 0x0000000000004000ull

+// The L1-D cache should be flushed after user accesses from the kernel +#define SEC_FTR_L1D_FLUSH_UACCESS 0x0000000000008000ull

// Features enabled by default #define SEC_FTR_DEFAULT \ @@ -94,6 +96,7 @@ static inline bool security_ftr_enabled(unsigned long feature) SEC_FTR_L1D_FLUSH_PR | \ SEC_FTR_BNDS_CHK_SPEC_BAR | \ SEC_FTR_L1D_FLUSH_ENTRY | \ + SEC_FTR_L1D_FLUSH_UACCESS | \ SEC_FTR_FAVOUR_SECURITY)

#endif /* _ASM_POWERPC_SECURITY_FEATURES_H */ diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h index 26b55f23cf64..1ccf474f08ab 100644 --- a/arch/powerpc/include/asm/setup.h +++ b/arch/powerpc/include/asm/setup.h @@ -46,6 +46,7 @@ void setup_barrier_nospec(void); #else static inline void setup_barrier_nospec(void) { }; #endif +void do_uaccess_flush_fixups(enum l1d_flush_type types); void do_entry_flush_fixups(enum l1d_flush_type types); void do_barrier_nospec_fixups(bool enable); extern bool barrier_nospec_enabled; diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 7715fd89bb94..7f8e1bdbe3e2 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1630,14 +1630,9 @@ stf_barrier_fallback: .endr blr

- .globl rfi_flush_fallback -rfi_flush_fallback: - SET_SCRATCH0(r13); - GET_PACA(r13); - std r9,PACA_EXRFI+EX_R9(r13) - std r10,PACA_EXRFI+EX_R10(r13) - std r11,PACA_EXRFI+EX_R11(r13) - mfctr r9 + +/* Clobbers r10, r11, ctr */ +.macro L1D_DISPLACEMENT_FLUSH ld r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13) ld r11,PACA_L1D_FLUSH_SIZE(r13) srdi r11,r11,(7 + 3) /* 128 byte lines, unrolled 8x */ @@ -1663,7 +1658,18 @@ rfi_flush_fallback: ld r11,(0x80 + 8)*7(r10) addi r10,r10,0x80*8 bdnz 1b +.endm +

+ .globl rfi_flush_fallback +rfi_flush_fallback: + SET_SCRATCH0(r13); + GET_PACA(r13); + std r9,PACA_EXRFI+EX_R9(r13) + std r10,PACA_EXRFI+EX_R10(r13) + std r11,PACA_EXRFI+EX_R11(r13) + mfctr r9 + L1D_DISPLACEMENT_FLUSH mtctr r9 ld r9,PACA_EXRFI+EX_R9(r13) ld r10,PACA_EXRFI+EX_R10(r13) @@ -1679,32 +1685,7 @@ hrfi_flush_fallback: std r10,PACA_EXRFI+EX_R10(r13) std r11,PACA_EXRFI+EX_R11(r13) mfctr r9 - ld r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13) - ld r11,PACA_L1D_FLUSH_SIZE(r13) - srdi r11,r11,(7 + 3) /* 128 byte lines, unrolled 8x */ - mtctr r11 - DCBT_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */ - - /* order ld/st prior to dcbt stop all streams with flushing */ - sync - - /* - * The load adresses are at staggered offsets within cachelines, - * which suits some pipelines better (on others it should not - * hurt). - */ -1: - ld r11,(0x80 + 8)*0(r10) - ld r11,(0x80 + 8)*1(r10) - ld r11,(0x80 + 8)*2(r10) - ld r11,(0x80 + 8)*3(r10) - ld r11,(0x80 + 8)*4(r10) - ld r11,(0x80 + 8)*5(r10) - ld r11,(0x80 + 8)*6(r10) - ld r11,(0x80 + 8)*7(r10) - addi r10,r10,0x80*8 - bdnz 1b - + L1D_DISPLACEMENT_FLUSH mtctr r9 ld r9,PACA_EXRFI+EX_R9(r13) ld r10,PACA_EXRFI+EX_R10(r13) @@ -1718,38 +1699,14 @@ entry_flush_fallback: std r10,PACA_EXRFI+EX_R10(r13) std r11,PACA_EXRFI+EX_R11(r13) mfctr r9 - ld r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13) - ld r11,PACA_L1D_FLUSH_SIZE(r13) - srdi r11,r11,(7 + 3) /* 128 byte lines, unrolled 8x */ - mtctr r11 - DCBT_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */ - - /* order ld/st prior to dcbt stop all streams with flushing */ - sync - - /* - * The load addresses are at staggered offsets within cachelines, - * which suits some pipelines better (on others it should not - * hurt). - */ -1: - ld r11,(0x80 + 8)*0(r10) - ld r11,(0x80 + 8)*1(r10) - ld r11,(0x80 + 8)*2(r10) - ld r11,(0x80 + 8)*3(r10) - ld r11,(0x80 + 8)*4(r10) - ld r11,(0x80 + 8)*5(r10) - ld r11,(0x80 + 8)*6(r10) - ld r11,(0x80 + 8)*7(r10) - addi r10,r10,0x80*8 - bdnz 1b - + L1D_DISPLACEMENT_FLUSH mtctr r9 ld r9,PACA_EXRFI+EX_R9(r13) ld r10,PACA_EXRFI+EX_R10(r13) ld r11,PACA_EXRFI+EX_R11(r13) blr

+ /* * Hash table stuff */ @@ -1909,3 +1866,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_CFAR) 1: addi r3,r1,STACK_FRAME_OVERHEAD bl kernel_bad_stack b 1b + +_KPROBE(do_uaccess_flush) + UACCESS_FLUSH_FIXUP_SECTION + nop + nop + nop + blr + L1D_DISPLACEMENT_FLUSH + blr diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c index b92debacb821..80eb47113d5d 100644 --- a/arch/powerpc/kernel/ppc_ksyms.c +++ b/arch/powerpc/kernel/ppc_ksyms.c @@ -6,6 +6,9 @@ #include <asm/cacheflush.h> #include <asm/epapr_hcalls.h> #include <asm/uaccess.h> +#ifdef CONFIG_PPC64 +#include <asm/book3s/64/kup-radix.h> +#endif

EXPORT_SYMBOL(flush_dcache_range); EXPORT_SYMBOL(flush_icache_range); @@ -46,3 +49,7 @@ EXPORT_SYMBOL(epapr_hypercall_start); EXPORT_SYMBOL(current_stack_pointer);

EXPORT_SYMBOL(__arch_clear_user); + +#ifdef CONFIG_PPC64 +EXPORT_SYMBOL(do_uaccess_flush); +#endif diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index cd405eaffa23..3c6717569360 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -845,8 +845,12 @@ static enum l1d_flush_type enabled_flush_types; static void *l1d_flush_fallback_area; static bool no_rfi_flush; static bool no_entry_flush; +static bool no_uaccess_flush; bool rfi_flush; bool entry_flush; +bool uaccess_flush; +DEFINE_STATIC_KEY_FALSE(uaccess_flush_key); +EXPORT_SYMBOL(uaccess_flush_key);

static int __init handle_no_rfi_flush(char *p) { @@ -864,6 +868,14 @@ static int __init handle_no_entry_flush(char *p) } early_param("no_entry_flush", handle_no_entry_flush);

+static int __init handle_no_uaccess_flush(char *p) +{ + pr_info("uaccess-flush: disabled on command line."); + no_uaccess_flush = true; + return 0; +} +early_param("no_uaccess_flush", handle_no_uaccess_flush); + /* * The RFI flush is not KPTI, but because users will see doco that says to use * nopti we hijack that option here to also disable the RFI flush. @@ -907,6 +919,23 @@ void entry_flush_enable(bool enable) entry_flush = enable; }

+void uaccess_flush_enable(bool enable) +{ + if (enable) { + do_uaccess_flush_fixups(enabled_flush_types); + if (static_key_initialized) + static_branch_enable(&uaccess_flush_key); + else + printk(KERN_DEBUG "uaccess-flush: deferring static key until after static key initialization\n"); + on_each_cpu(do_nothing, NULL, 1); + } else { + static_branch_disable(&uaccess_flush_key); + do_uaccess_flush_fixups(L1D_FLUSH_NONE); + } + + uaccess_flush = enable; +} + static void __ref init_fallback_flush(void) { u64 l1d_size, limit; @@ -961,6 +990,15 @@ void setup_entry_flush(bool enable) entry_flush_enable(enable); }

+void setup_uaccess_flush(bool enable) +{ + if (cpu_mitigations_off()) + return; + + if (!no_uaccess_flush) + uaccess_flush_enable(enable); +} + #ifdef CONFIG_DEBUG_FS static int rfi_flush_set(void *data, u64 val) { @@ -1014,12 +1052,54 @@ static int entry_flush_get(void *data, u64 *val)

DEFINE_SIMPLE_ATTRIBUTE(fops_entry_flush, entry_flush_get, entry_flush_set, "%llu\n");

+static int uaccess_flush_set(void *data, u64 val) +{ + bool enable; + + if (val == 1) + enable = true; + else if (val == 0) + enable = false; + else + return -EINVAL; + + /* Only do anything if we're changing state */ + if (enable != uaccess_flush) + uaccess_flush_enable(enable); + + return 0; +} + +static int uaccess_flush_get(void *data, u64 *val) +{ + *val = uaccess_flush ? 1 : 0; + return 0; +} + +DEFINE_SIMPLE_ATTRIBUTE(fops_uaccess_flush, uaccess_flush_get, uaccess_flush_set, "%llu\n"); + + static __init int rfi_flush_debugfs_init(void) { debugfs_create_file("rfi_flush", 0600, powerpc_debugfs_root, NULL, &fops_rfi_flush); debugfs_create_file("entry_flush", 0600, powerpc_debugfs_root, NULL, &fops_entry_flush); + debugfs_create_file("uaccess_flush", 0600, powerpc_debugfs_root, NULL, &fops_uaccess_flush); return 0; } device_initcall(rfi_flush_debugfs_init); #endif + +/* + * setup_uaccess_flush runs before jump_label_init, so we can't do the setup + * there. Do it now instead. + */ +static __init int uaccess_flush_static_key_init(void) +{ + if (uaccess_flush) { + printk(KERN_DEBUG "uaccess-flush: switching on static key\n"); + static_branch_enable(&uaccess_flush_key); + } + return 0; +} +early_initcall(uaccess_flush_static_key_init); #endif /* CONFIG_PPC_BOOK3S_64 */ diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index 43a8cfa5e2fb..f820d03335eb 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -80,6 +80,13 @@ SECTIONS __stop___stf_entry_barrier_fixup = .; }

+ . = ALIGN(8); + __uaccess_flush_fixup : AT(ADDR(__uaccess_flush_fixup) - LOAD_OFFSET) { + __start___uaccess_flush_fixup = .; + *(__uaccess_flush_fixup) + __stop___uaccess_flush_fixup = .; + } + . = ALIGN(8); __entry_flush_fixup : AT(ADDR(__entry_flush_fixup) - LOAD_OFFSET) { __start___entry_flush_fixup = .; diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 4f13bba13596..40b134bf5a68 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -229,6 +229,56 @@ void do_stf_barrier_fixups(enum stf_barrier_type types) do_stf_exit_barrier_fixups(types); }

+void do_uaccess_flush_fixups(enum l1d_flush_type types) +{ + unsigned int instrs[4], *dest; + long *start, *end; + int i; + + start = PTRRELOC(&__start___uaccess_flush_fixup); + end = PTRRELOC(&__stop___uaccess_flush_fixup); + + instrs[0] = 0x60000000; /* nop */ + instrs[1] = 0x60000000; /* nop */ + instrs[2] = 0x60000000; /* nop */ + instrs[3] = 0x4e800020; /* blr */ + + i = 0; + if (types == L1D_FLUSH_FALLBACK) { + instrs[3] = 0x60000000; /* nop */ + /* fallthrough to fallback flush */ + } + + if (types & L1D_FLUSH_ORI) { + instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */ + instrs[i++] = 0x63de0000; /* ori 30,30,0 L1d flush*/ + } + + if (types & L1D_FLUSH_MTTRIG) + instrs[i++] = 0x7c12dba6; /* mtspr TRIG2,r0 (SPR #882) */ + + for (i = 0; start < end; start++, i++) { + dest = (void *)start + *start; + + pr_devel("patching dest %lx\n", (unsigned long)dest); + + patch_instruction(dest, instrs[0]); + + patch_instruction((dest + 1), instrs[1]); + patch_instruction((dest + 2), instrs[2]); + patch_instruction((dest + 3), instrs[3]); + } + + printk(KERN_DEBUG "uaccess-flush: patched %d locations (%s flush)\n", i, + (types == L1D_FLUSH_NONE) ? "no" : + (types == L1D_FLUSH_FALLBACK) ? "fallback displacement" : + (types & L1D_FLUSH_ORI) ? (types & L1D_FLUSH_MTTRIG) + ? "ori+mttrig type" + : "ori type" : + (types & L1D_FLUSH_MTTRIG) ? "mttrig type" + : "unknown"); +} + void do_entry_flush_fixups(enum l1d_flush_type types) { unsigned int instrs[3], *dest; diff --git a/arch/powerpc/platforms/powernv/setup.c b/arch/powerpc/platforms/powernv/setup.c index fe3f1f438f78..6259228a0e18 100644 --- a/arch/powerpc/platforms/powernv/setup.c +++ b/arch/powerpc/platforms/powernv/setup.c @@ -126,9 +126,10 @@ static void pnv_setup_rfi_flush(void)

/* * 4.4 doesn't support Power9 bare metal, so we don't need to flush - * here - the flush fixes a P9 specific vulnerability. + * here - the flushes fix a P9 specific vulnerability. */ security_ftr_clear(SEC_FTR_L1D_FLUSH_ENTRY); + security_ftr_clear(SEC_FTR_L1D_FLUSH_UACCESS);

enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) && \ (security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR) || \ @@ -140,6 +141,10 @@ static void pnv_setup_rfi_flush(void) enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) && security_ftr_enabled(SEC_FTR_L1D_FLUSH_ENTRY); setup_entry_flush(enable); + + enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) && + security_ftr_enabled(SEC_FTR_L1D_FLUSH_UACCESS); + setup_uaccess_flush(enable); }

static void __init pnv_setup_arch(void) diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index 69f1808ecbd2..498c5092bd23 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -588,6 +588,10 @@ void pseries_setup_rfi_flush(void) enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) && security_ftr_enabled(SEC_FTR_L1D_FLUSH_ENTRY); setup_entry_flush(enable); + + enable = security_ftr_enabled(SEC_FTR_FAVOUR_SECURITY) && + security_ftr_enabled(SEC_FTR_L1D_FLUSH_UACCESS); + setup_uaccess_flush(enable); }

static void __init pSeries_setup_arch(void)