From: Ard Biesheuvel ardb@kernel.org
commit f77ac2e378be9dd61eb88728f0840642f045d9d1 upstream.
There are a couple of problems with the exception entry code that deals with FP exceptions (which are reported as UND exceptions) when building the kernel in Thumb2 mode: - the conditional branch to vfp_kmode_exception in vfp_support_entry() may be out of range for its target, depending on how the linker decides to arrange the sections; - when the UND exception is taken in kernel mode, the emulation handling logic is entered via the 'call_fpe' label, which means we end up using the wrong value/mask pairs to match and detect the NEON opcodes.
Since UND exceptions in kernel mode are unlikely to occur on a hot path (as opposed to the user mode version which is invoked for VFP support code and lazy restore), we can use the existing undef hook machinery for any kernel mode instruction emulation that is needed, including calling the existing vfp_kmode_exception() routine for unexpected cases. So drop the call to call_fpe, and instead, install an undef hook that will get called for NEON and VFP instructions that trigger an UND exception in kernel mode.
While at it, make sure that the PC correction is accurate for the execution mode where the exception was taken, by checking the PSR Thumb bit.
Cc: Dmitry Osipenko digetx@gmail.com Cc: Kees Cook keescook@chromium.org Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections") Signed-off-by: Ard Biesheuvel ardb@kernel.org Reviewed-by: Linus Walleij linus.walleij@linaro.org Reviewed-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Russell King rmk+kernel@armlinux.org.uk [nd: fix conflict in arch/arm/vfp/vfphw.S due to missing commit 2cbd1cc3dcd3 ("ARM: 8991/1: use VFP assembler mnemonics if available")] Signed-off-by: Nick Desaulniers ndesaulniers@google.com --- This should have been sent along with https://lore.kernel.org/stable/20210113185758.GA571703@ubuntu-m3-large-x86/ it's my fault I missed it.
arch/arm/kernel/entry-armv.S | 25 ++---------------- arch/arm/vfp/vfphw.S | 5 ---- arch/arm/vfp/vfpmodule.c | 49 ++++++++++++++++++++++++++++++++++-- 3 files changed, 49 insertions(+), 30 deletions(-)
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S index a874b753397e..b62d74a2c73a 100644 --- a/arch/arm/kernel/entry-armv.S +++ b/arch/arm/kernel/entry-armv.S @@ -252,31 +252,10 @@ __und_svc: #else svc_entry #endif - @ - @ call emulation code, which returns using r9 if it has emulated - @ the instruction, or the more conventional lr if we are to treat - @ this as a real undefined instruction - @ - @ r0 - instruction - @ -#ifndef CONFIG_THUMB2_KERNEL - ldr r0, [r4, #-4] -#else - mov r1, #2 - ldrh r0, [r4, #-2] @ Thumb instruction at LR - 2 - cmp r0, #0xe800 @ 32-bit instruction if xx >= 0 - blo __und_svc_fault - ldrh r9, [r4] @ bottom 16 bits - add r4, r4, #2 - str r4, [sp, #S_PC] - orr r0, r9, r0, lsl #16 -#endif - badr r9, __und_svc_finish - mov r2, r4 - bl call_fpe
mov r1, #4 @ PC correction to apply -__und_svc_fault: + THUMB( tst r5, #PSR_T_BIT ) @ exception taken in Thumb mode? + THUMB( movne r1, #2 ) @ if so, fix up PC correction mov r0, sp @ struct pt_regs *regs bl __und_fault
diff --git a/arch/arm/vfp/vfphw.S b/arch/arm/vfp/vfphw.S index b2e560290860..b530db8f2c6c 100644 --- a/arch/arm/vfp/vfphw.S +++ b/arch/arm/vfp/vfphw.S @@ -78,11 +78,6 @@ ENTRY(vfp_support_entry) DBGSTR3 "instr %08x pc %08x state %p", r0, r2, r10
- ldr r3, [sp, #S_PSR] @ Neither lazy restore nor FP exceptions - and r3, r3, #MODE_MASK @ are supported in kernel mode - teq r3, #USR_MODE - bne vfp_kmode_exception @ Returns through lr - VFPFMRX r1, FPEXC @ Is the VFP enabled? DBGSTR1 "fpexc %08x", r1 tst r1, #FPEXC_EN diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 8c9e7f9f0277..c3b6451c18bd 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -23,6 +23,7 @@ #include <asm/cputype.h> #include <asm/system_info.h> #include <asm/thread_notify.h> +#include <asm/traps.h> #include <asm/vfp.h>
#include "vfpinstr.h" @@ -642,7 +643,9 @@ static int vfp_starting_cpu(unsigned int unused) return 0; }
-void vfp_kmode_exception(void) +#ifdef CONFIG_KERNEL_MODE_NEON + +static int vfp_kmode_exception(struct pt_regs *regs, unsigned int instr) { /* * If we reach this point, a floating point exception has been raised @@ -660,9 +663,51 @@ void vfp_kmode_exception(void) pr_crit("BUG: unsupported FP instruction in kernel mode\n"); else pr_crit("BUG: FP instruction issued in kernel mode with FP unit disabled\n"); + pr_crit("FPEXC == 0x%08x\n", fmrx(FPEXC)); + return 1; }
-#ifdef CONFIG_KERNEL_MODE_NEON +static struct undef_hook vfp_kmode_exception_hook[] = {{ + .instr_mask = 0xfe000000, + .instr_val = 0xf2000000, + .cpsr_mask = MODE_MASK | PSR_T_BIT, + .cpsr_val = SVC_MODE, + .fn = vfp_kmode_exception, +}, { + .instr_mask = 0xff100000, + .instr_val = 0xf4000000, + .cpsr_mask = MODE_MASK | PSR_T_BIT, + .cpsr_val = SVC_MODE, + .fn = vfp_kmode_exception, +}, { + .instr_mask = 0xef000000, + .instr_val = 0xef000000, + .cpsr_mask = MODE_MASK | PSR_T_BIT, + .cpsr_val = SVC_MODE | PSR_T_BIT, + .fn = vfp_kmode_exception, +}, { + .instr_mask = 0xff100000, + .instr_val = 0xf9000000, + .cpsr_mask = MODE_MASK | PSR_T_BIT, + .cpsr_val = SVC_MODE | PSR_T_BIT, + .fn = vfp_kmode_exception, +}, { + .instr_mask = 0x0c000e00, + .instr_val = 0x0c000a00, + .cpsr_mask = MODE_MASK, + .cpsr_val = SVC_MODE, + .fn = vfp_kmode_exception, +}}; + +static int __init vfp_kmode_exception_hook_init(void) +{ + int i; + + for (i = 0; i < ARRAY_SIZE(vfp_kmode_exception_hook); i++) + register_undef_hook(&vfp_kmode_exception_hook[i]); + return 0; +} +core_initcall(vfp_kmode_exception_hook_init);
/* * Kernel-side NEON support functions