diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2025-02-13 12:45:47 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2025-02-14 10:32:07 +0100 |
| commit | 882b86fd4e0d49bf91148dbadcdbece19ded40e6 (patch) | |
| tree | ba69be9524df4fc5caa67530d871acfe3ad93113 /arch/x86/kernel | |
| parent | 306859de59e59f88662b6b56ff2ce3bbb1e375bb (diff) | |
x86/ibt: Handle FineIBT in handle_cfi_failure()
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.net
Diffstat (limited to 'arch/x86/kernel')
| -rw-r--r-- | arch/x86/kernel/alternative.c | 30 | ||||
| -rw-r--r-- | arch/x86/kernel/cfi.c | 22 |
2 files changed, 48 insertions, 4 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index e285933506e9..247ee5ffbff4 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1065,6 +1065,7 @@ 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" @@ -1072,9 +1073,11 @@ 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" @@ -1410,6 +1413,33 @@ static void poison_cfi(void *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 e6bf78fac146..f6905bef0af8 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); } |