diff options
| author | Peter Zijlstra <[email protected]> | 2022-11-14 16:23:45 +0100 |
|---|---|---|
| committer | Josh Poimboeuf <[email protected]> | 2023-06-07 09:27:11 -0700 |
| commit | 4a03aa34432abe0703abf232f31fc5e2ed8256f6 (patch) | |
| tree | bfde124225e6c7cd2eb18dd17e6c197b62d6059c | |
| parent | d49d1666aab51ad3caf79f414aff6b641837a6ea (diff) | |
lkdtm: Avoid objtool/ibt warning
For certain configs objtool will complain like:
vmlinux.o: warning: objtool: lkdtm_UNSET_SMEP+0x1c3: relocation to !ENDBR: native_write_cr4+0x41
What happens is that GCC optimizes the loop:
insn = (unsigned char *)native_write_cr4;
for (i = 0; i < MOV_CR4_DEPTH; i++)
to read something like:
for (insn = (unsigned char *)native_write_cr4;
insn < (unsigned char *)native_write_cr4 + MOV_CR4_DEPTH;
insn++)
Which then obviously generates the text reference
native_write_cr4+041. Since none of this is a fast path, simply
confuse GCC enough to inhibit this optimization.
Reported-by: kernel test robot <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Josh Poimboeuf <[email protected]>
| -rw-r--r-- | drivers/misc/lkdtm/bugs.c | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 48821f4c2b21..92110cb6a0eb 100644 --- a/drivers/misc/lkdtm/bugs.c +++ b/drivers/misc/lkdtm/bugs.c @@ -487,6 +487,7 @@ static void lkdtm_UNSET_SMEP(void) * the cr4 writing instruction. */ insn = (unsigned char *)native_write_cr4; + OPTIMIZER_HIDE_VAR(insn); for (i = 0; i < MOV_CR4_DEPTH; i++) { /* mov %rdi, %cr4 */ if (insn[i] == 0x0f && insn[i+1] == 0x22 && insn[i+2] == 0xe7) |