[PATCH 5.15 3/5] x86/alternatives: Introduce int3_emulate_jcc()

Thadeu Lima de Souza Cascardo
2024-03-13T10:43:31Z

From: Peter Zijlstra <peterz@infradead.org>

commit db7adcfd1cec4e95155e37bc066fddab302c6340 upstream.

Move the kprobe Jcc emulation into int3_emulate_jcc() so it can be
used by more code -- specifically static_call() will need this.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20230123210607.057678245@infradead.org
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
---
arch/x86/include/asm/text-patching.h | 31 +++++++++++++++++++++++
arch/x86/kernel/kprobes/core.c | 38 ++++++----------------------
2 files changed, 39 insertions(+), 30 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index c6015b407461..7281ce64e99d 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -181,6 +181,37 @@ void int3_emulate_ret(struct pt_regs *regs)
unsigned long ip = int3_emulate_pop(regs);
int3_emulate_jmp(regs, ip);
}
+
+static __always_inline
+void int3_emulate_jcc(struct pt_regs *regs, u8 cc, unsigned long ip, unsigned long disp)
+{
+ static const unsigned long jcc_mask[6] = {
+ [0] = X86_EFLAGS_OF,
+ [1] = X86_EFLAGS_CF,
+ [2] = X86_EFLAGS_ZF,
+ [3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
+ [4] = X86_EFLAGS_SF,
+ [5] = X86_EFLAGS_PF,
+ };
+
+ bool invert = cc & 1;
+ bool match;
+
+ if (cc < 0xc) {
+ match = regs->flags & jcc_mask[cc >> 1];
+ } else {
+ match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
+ ((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
+ if (cc >= 0xe)
+ match = match || (regs->flags & X86_EFLAGS_ZF);
+ }
+
+ if ((match && !invert) || (!match && invert))
+ ip += disp;
+
+ int3_emulate_jmp(regs, ip);
+}
+
#endif /* !CONFIG_UML_X86 */

#endif /* _ASM_X86_TEXT_PATCHING_H */
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 052ea7425c4d..893f040b97b7 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -463,50 +463,26 @@ static void kprobe_emulate_call(struct kprobe *p, struct pt_regs *regs)
}
NOKPROBE_SYMBOL(kprobe_emulate_call);

-static nokprobe_inline
-void __kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs, bool cond)
+static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
{
unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;

- if (cond)
- ip += p->ainsn.rel32;
+ ip += p->ainsn.rel32;
int3_emulate_jmp(regs, ip);
}
-
-static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
-{
- __kprobe_emulate_jmp(p, regs, true);
-}
NOKPROBE_SYMBOL(kprobe_emulate_jmp);

-static const unsigned long jcc_mask[6] = {
- [0] = X86_EFLAGS_OF,
- [1] = X86_EFLAGS_CF,
- [2] = X86_EFLAGS_ZF,
- [3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
- [4] = X86_EFLAGS_SF,
- [5] = X86_EFLAGS_PF,
-};
-
static void kprobe_emulate_jcc(struct kprobe *p, struct pt_regs *regs)
{
- bool invert = p->ainsn.jcc.type & 1;
- bool match;
+ unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;

- if (p->ainsn.jcc.type < 0xc) {
- match = regs->flags & jcc_mask[p->ainsn.jcc.type >> 1];
- } else {
- match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
- ((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
- if (p->ainsn.jcc.type >= 0xe)
- match = match || (regs->flags & X86_EFLAGS_ZF);
- }
- __kprobe_emulate_jmp(p, regs, (match && !invert) || (!match && invert));
+ int3_emulate_jcc(regs, p->ainsn.jcc.type, ip, p->ainsn.rel32);
}
NOKPROBE_SYMBOL(kprobe_emulate_jcc);

static void kprobe_emulate_loop(struct kprobe *p, struct pt_regs *regs)
{
+ unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
bool match;

if (p->ainsn.loop.type != 3) { /* LOOP* */
@@ -534,7 +510,9 @@ static void kprobe_emulate_loop(struct kprobe *p, struct pt_regs *regs)
else if (p->ainsn.loop.type == 1) /* LOOPE */
match = match && (regs->flags & X86_EFLAGS_ZF);

- __kprobe_emulate_jmp(p, regs, match);
+ if (match)
+ ip += p->ainsn.rel32;
+ int3_emulate_jmp(regs, ip);
}
NOKPROBE_SYMBOL(kprobe_emulate_loop);

--
2.34.1