From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 882b86fd4e0d49bf91148dbadcdbece19ded40e6 ]
Sami reminded me that FineIBT failure does not hook into the regular CFI failure case, and as such CFI_PERMISSIVE does not work.
Reported-by: Sami Tolvanen samitolvanen@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Sami Tolvanen samitolvanen@google.com Link: https://lkml.kernel.org/r/20250214092619.GB21726@noisy.programming.kicks-ass... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/cfi.h | 11 +++++++++++ arch/x86/kernel/alternative.c | 30 ++++++++++++++++++++++++++++++ arch/x86/kernel/cfi.c | 22 ++++++++++++++++++---- 3 files changed, 59 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/cfi.h b/arch/x86/include/asm/cfi.h index 31d19c815f992..7dd5ab239c87b 100644 --- a/arch/x86/include/asm/cfi.h +++ b/arch/x86/include/asm/cfi.h @@ -126,6 +126,17 @@ static inline int cfi_get_offset(void)
extern u32 cfi_get_func_hash(void *func);
+#ifdef CONFIG_FINEIBT +extern bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 *type); +#else +static inline bool +decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 *type) +{ + return false; +} + +#endif + #else static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) { diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index c71b575bf2292..f9ada11c910e1 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1080,6 +1080,7 @@ asm( ".pushsection .rodata \n" " endbr64 \n" " subl $0x12345678, %r10d \n" " je fineibt_preamble_end \n" + "fineibt_preamble_ud2: \n" " ud2 \n" " nop \n" "fineibt_preamble_end: \n" @@ -1087,9 +1088,11 @@ asm( ".pushsection .rodata \n" );
extern u8 fineibt_preamble_start[]; +extern u8 fineibt_preamble_ud2[]; extern u8 fineibt_preamble_end[];
#define fineibt_preamble_size (fineibt_preamble_end - fineibt_preamble_start) +#define fineibt_preamble_ud2 (fineibt_preamble_ud2 - fineibt_preamble_start) #define fineibt_preamble_hash 7
asm( ".pushsection .rodata \n" @@ -1407,6 +1410,33 @@ static void poison_cfi(void *addr, void *wr_addr) } }
+/* + * regs->ip points to a UD2 instruction, return true and fill out target and + * type when this UD2 is from a FineIBT preamble. + * + * We check the preamble by checking for the ENDBR instruction relative to the + * UD2 instruction. + */ +bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 *type) +{ + unsigned long addr = regs->ip - fineibt_preamble_ud2; + u32 endbr, hash; + + __get_kernel_nofault(&endbr, addr, u32, Efault); + if (endbr != gen_endbr()) + return false; + + *target = addr + fineibt_preamble_size; + + __get_kernel_nofault(&hash, addr + fineibt_preamble_hash, u32, Efault); + *type = (u32)regs->r10 + hash; + + return true; + +Efault: + return false; +} + #else
static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline, diff --git a/arch/x86/kernel/cfi.c b/arch/x86/kernel/cfi.c index e6bf78fac1462..f6905bef0af84 100644 --- a/arch/x86/kernel/cfi.c +++ b/arch/x86/kernel/cfi.c @@ -70,11 +70,25 @@ enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) unsigned long target; u32 type;
- if (!is_cfi_trap(regs->ip)) - return BUG_TRAP_TYPE_NONE; + switch (cfi_mode) { + case CFI_KCFI: + if (!is_cfi_trap(regs->ip)) + return BUG_TRAP_TYPE_NONE; + + if (!decode_cfi_insn(regs, &target, &type)) + return report_cfi_failure_noaddr(regs, regs->ip); + + break;
- if (!decode_cfi_insn(regs, &target, &type)) - return report_cfi_failure_noaddr(regs, regs->ip); + case CFI_FINEIBT: + if (!decode_fineibt_insn(regs, &target, &type)) + return BUG_TRAP_TYPE_NONE; + + break; + + default: + return BUG_TRAP_TYPE_NONE; + }
return report_cfi_failure(regs, regs->ip, &target, type); }