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[ELF] Change the size of ibtplt from 24 bytes to 32 bytes

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This commit is contained in:
Rui Ueyama 2022-02-22 16:13:45 +09:00
parent 3f9868238b
commit 4667be6134
3 changed files with 15 additions and 7 deletions
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10
elf/arch-x86-64.cc
View File

@ -24,8 +24,8 @@ static void write_compact_plt(Context<E> &ctx) {
// The IBTPLT is a security-enhanced version of the regular PLT.
// It uses Indirect Branch Tracking (IBT) feature which is part of
// Intel Control-Flow Enforcement (CET). IBTPLT is slightly larger
// than the regular PLT (24 bytes vs 16 bytes for each entry).
// Intel Control-Flow Enforcement (CET). IBTPLT is larger than the
// regular PLT (32 bytes vs 16 bytes for each entry).
//
// Note that our IBTPLT instruction sequence is different from the one
// used in GNU ld. GNU's IBTPLT implementation uses two separate
@ -48,12 +48,18 @@ static void write_ibtplt(Context<E> &ctx) {
// Write PLT entries
i64 relplt_idx = 0;
// The last 11 bytes are padding, so we could have shrunk each PLT
// entry to 24 bytes. We don't do that because according to the Intel
// optimization manual, all branch targets should be 16-byte aligned
// for optimal performance.
static const u8 data[] = {
0xf3, 0x0f, 0x1e, 0xfa, // endbr64
0xff, 0x25, 0, 0, 0, 0, // jmp *foo@GOTPLT
0x68, 0, 0, 0, 0, // push $index_in_relplt
0xf2, 0xe9, 0, 0, 0, 0, // jmp PLT[0]
0x0f, 0x1f, 0x00, // nop
0x0f, 0x1f, 0x40, 0x00, // nop
0x0f, 0x1f, 0x40, 0x00, // nop
};
for (Symbol<E> *sym : ctx.plt->symbols) {

2
elf/cmdline.cc
View File

@ -382,7 +382,7 @@ static std::pair<i64, i64> get_plt_size(Context<E> &ctx) {
if (ctx.arg.z_now)
return {0, 8};
if (ctx.arg.z_ibtplt)
return {16, 24};
return {16, 32};
return {16, 16};
case EM_386:
return {16, 16};

10
test/elf/z-ibtplt.sh
View File

@ -14,9 +14,8 @@ mkdir -p $t
cat <<EOF | $CC -fPIC -o $t/a.o -c -xc -
#include <stdio.h>
void hello() {
printf("Hello");
}
void hello() { printf("Hello"); }
void world() { printf("world"); }
EOF
$CC -B. -o $t/b.so -shared $t/a.o -Wl,-z,ibtplt
@ -25,10 +24,13 @@ cat <<EOF | $CC -o $t/c.o -c -xc -
#include <stdio.h>
void hello();
void world();
int main() {
hello();
puts(" world");
printf(" ");
world();
printf("\n");
}
EOF