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x86/alternative: Use .ibt_endbr_seal to seal indirect calls

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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
This commit is contained in:
Peter Zijlstra
2022-03-08 16:30:56 +01:00
parent 89bc853eae
commit ed53a0d971
8 changed files with 117 additions and 13 deletions
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10
scripts/link-vmlinux.sh
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@@ -108,7 +108,9 @@ objtool_link()
local objtoolcmd;
local objtoolopt;
if is_enabled CONFIG_LTO_CLANG && is_enabled CONFIG_STACK_VALIDATION; then
if is_enabled CONFIG_STACK_VALIDATION && \
( is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT ); then
# Don't perform vmlinux validation unless explicitly requested,
# but run objtool on vmlinux.o now that we have an object file.
if is_enabled CONFIG_UNWINDER_ORC; then
@@ -117,6 +119,10 @@ objtool_link()
objtoolopt="${objtoolopt} --lto"
if is_enabled CONFIG_X86_KERNEL_IBT; then
objtoolopt="${objtoolopt} --ibt"
fi
if is_enabled CONFIG_FTRACE_MCOUNT_USE_OBJTOOL; then
objtoolopt="${objtoolopt} --mcount"
fi
@@ -168,7 +174,7 @@ vmlinux_link()
# skip output file argument
shift
if is_enabled CONFIG_LTO_CLANG; then
if is_enabled CONFIG_LTO_CLANG || is_enabled CONFIG_X86_KERNEL_IBT; then
# Use vmlinux.o instead of performing the slow LTO link again.
objs=vmlinux.o
libs=