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Subject[PATCH v7 12/18] x86/alternatives: Teach text_poke_bp() to emulate RET
Future patches will need to poke a RET instruction, provide the
infrastructure required for this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
arch/x86/include/asm/text-patching.h | 19 +++++++++++++++++++
arch/x86/kernel/alternative.c | 5 +++++
2 files changed, 24 insertions(+)

--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -53,6 +53,9 @@ extern void text_poke_finish(void);
#define INT3_INSN_SIZE 1
#define INT3_INSN_OPCODE 0xCC

+#define RET_INSN_SIZE 1
+#define RET_INSN_OPCODE 0xC3
+
#define CALL_INSN_SIZE 5
#define CALL_INSN_OPCODE 0xE8

@@ -73,6 +76,7 @@ static __always_inline int text_opcode_s

switch(opcode) {
__CASE(INT3);
+ __CASE(RET);
__CASE(CALL);
__CASE(JMP32);
__CASE(JMP8);
@@ -141,11 +145,26 @@ void int3_emulate_push(struct pt_regs *r
}

static __always_inline
+unsigned long int3_emulate_pop(struct pt_regs *regs)
+{
+ unsigned long val = *(unsigned long *)regs->sp;
+ regs->sp += sizeof(unsigned long);
+ return val;
+}
+
+static __always_inline
void int3_emulate_call(struct pt_regs *regs, unsigned long func)
{
int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
int3_emulate_jmp(regs, func);
}
+
+static __always_inline
+void int3_emulate_ret(struct pt_regs *regs)
+{
+ unsigned long ip = int3_emulate_pop(regs);
+ int3_emulate_jmp(regs, ip);
+}
#endif /* !CONFIG_UML_X86 */

#endif /* _ASM_X86_TEXT_PATCHING_H */
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1099,6 +1099,10 @@ int noinstr poke_int3_handler(struct pt_
*/
goto out_put;

+ case RET_INSN_OPCODE:
+ int3_emulate_ret(regs);
+ break;
+
case CALL_INSN_OPCODE:
int3_emulate_call(regs, (long)ip + tp->rel32);
break;
@@ -1240,6 +1244,7 @@ static void text_poke_loc_init(struct te

switch (tp->opcode) {
case INT3_INSN_OPCODE:
+ case RET_INSN_OPCODE:
break;

case CALL_INSN_OPCODE:

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