diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-03-08 16:30:56 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-03-15 10:32:47 +0100 |
| commit | ed53a0d971926e484d86cce617ec02a7ee85c3fe (patch) | |
| tree | 1423484f3912113c56c0b77fa5b0397113040828 /arch/x86/include/asm/ibt.h | |
| parent | 89bc853eae4ad125030ef99f207ba76c2f00a26e (diff) | |
x86/alternative: Use .ibt_endbr_seal to seal indirect calls
Objtool's --ibt option generates .ibt_endbr_seal which lists
superfluous ENDBR instructions. That is those instructions for which
the function is never indirectly called.
Overwrite these ENDBR instructions with a NOP4 such that these
function can never be indirect called, reducing the number of viable
ENDBR targets in the kernel.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.822545231@infradead.org
Diffstat (limited to 'arch/x86/include/asm/ibt.h')
| -rw-r--r-- | arch/x86/include/asm/ibt.h | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h index 52fb05d66489..689880eca9ba 100644 --- a/arch/x86/include/asm/ibt.h +++ b/arch/x86/include/asm/ibt.h @@ -46,8 +46,20 @@ static inline __attribute_const__ u32 gen_endbr(void) return endbr; } +static inline __attribute_const__ u32 gen_endbr_poison(void) +{ + /* + * 4 byte NOP that isn't NOP4 (in fact it is OSP NOP3), such that it + * will be unique to (former) ENDBR sites. + */ + return 0x001f0f66; /* osp nopl (%rax) */ +} + static inline bool is_endbr(u32 val) { + if (val == gen_endbr_poison()) + return true; + val &= ~0x01000000U; /* ENDBR32 -> ENDBR64 */ return val == gen_endbr(); } |