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Subject[PATCH 10/13] x86/alternative: Support indirect call replacement
Date
Add alternative patching support for replacing an instruction with an
indirect call. This will be needed for the paravirt alternatives.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/alternative.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 3344d3382e91..81c577c7deba 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -410,20 +410,28 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
insnbuf_sz = a->replacementlen;

/*
- * 0xe8 is a relative jump; fix the offset.
- *
- * Instruction length is checked before the opcode to avoid
- * accessing uninitialized bytes for zero-length replacements.
+ * Fix the address offsets for call and jump instructions which
+ * use PC-relative addressing.
*/
if (a->replacementlen == 5 && *insnbuf == 0xe8) {
+ /* direct call */
*(s32 *)(insnbuf + 1) += replacement - instr;
- DPRINTK("Fix CALL offset: 0x%x, CALL 0x%lx",
+ DPRINTK("Fix direct CALL offset: 0x%x, CALL 0x%lx",
*(s32 *)(insnbuf + 1),
(unsigned long)instr + *(s32 *)(insnbuf + 1) + 5);
- }

- if (a->replacementlen && is_jmp(replacement[0]))
+ } else if (a->replacementlen == 6 && *insnbuf == 0xff &&
+ *(insnbuf+1) == 0x15) {
+ /* indirect call */
+ *(s32 *)(insnbuf + 2) += replacement - instr;
+ DPRINTK("Fix indirect CALL offset: 0x%x, CALL *0x%lx",
+ *(s32 *)(insnbuf + 2),
+ (unsigned long)instr + *(s32 *)(insnbuf + 2) + 6);
+
+ } else if (a->replacementlen && is_jmp(replacement[0])) {
+ /* direct jump */
recompute_jump(a, instr, replacement, insnbuf);
+ }

if (a->instrlen > a->replacementlen) {
add_nops(insnbuf + a->replacementlen,
--
2.13.6
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