Messages in this thread Patch in this message | | | Date | Fri, 09 Jun 2023 07:47:42 -0000 | From | "tip-bot2 for Peter Zijlstra" <> | Subject | [tip: objtool/core] lkdtm: Avoid objtool/ibt warning |
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The following commit has been merged into the objtool/core branch of tip:
Commit-ID: 4a03aa34432abe0703abf232f31fc5e2ed8256f6 Gitweb: https://git.kernel.org/tip/4a03aa34432abe0703abf232f31fc5e2ed8256f6 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 14 Nov 2022 16:23:45 +01:00 Committer: Josh Poimboeuf <jpoimboe@kernel.org> CommitterDate: Wed, 07 Jun 2023 09:27:11 -07:00
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 <lkp@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/Y3JdgbXRV0MNZ+9h@hirez.programming.kicks-ass.net Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> --- drivers/misc/lkdtm/bugs.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/misc/lkdtm/bugs.c b/drivers/misc/lkdtm/bugs.c index 48821f4..92110cb 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)
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