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Message-Id: <160726389867.3413805.17190350990123597258.stgit@devnote2>
Date: Sun, 6 Dec 2020 23:11:38 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Ingo Molnar <mingo@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>
Cc: mhiramat@...nel.org, linux-kernel@...r.kernel.org,
"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
David Miller <davem@...emloft.net>,
Borislav Petkov <bp@...en8.de>, x86@...nel.org
Subject: [PATCH 1/1] x86/kprobes: Do not decode opcode in resume_execution()
Currently kprobes x86 decodes opcode right after single
stepping in resume_execution(). But it already decoded the
opcode while preparing arch_specific_insn in arch_copy_kprobe().
This decodes opcode in arch_copy_kprobe() instead of
resume_execution() and sets some flags which classifies
the opcode for resuming process.
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
arch/x86/include/asm/kprobes.h | 11 ++-
arch/x86/kernel/kprobes/core.c | 166 ++++++++++++++++++----------------------
2 files changed, 80 insertions(+), 97 deletions(-)
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 991a7ad540c7..d20a3d6be36e 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -58,14 +58,17 @@ struct arch_specific_insn {
/* copy of the original instruction */
kprobe_opcode_t *insn;
/*
- * boostable = false: This instruction type is not boostable.
- * boostable = true: This instruction has been boosted: we have
+ * boostable = 0: This instruction type is not boostable.
+ * boostable = 1: This instruction has been boosted: we have
* added a relative jump after the instruction copy in insn,
* so no single-step and fixup are needed (unless there's
* a post_handler).
*/
- bool boostable;
- bool if_modifier;
+ unsigned boostable:1;
+ unsigned if_modifier:1;
+ unsigned is_call:1;
+ unsigned is_pushf:1;
+ unsigned is_abs_ip:1;
/* Number of bytes of text poked */
int tp_len;
};
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 547c7abb39f5..9d95f43363f1 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -132,26 +132,6 @@ void synthesize_relcall(void *dest, void *from, void *to)
}
NOKPROBE_SYMBOL(synthesize_relcall);
-/*
- * Skip the prefixes of the instruction.
- */
-static kprobe_opcode_t *skip_prefixes(kprobe_opcode_t *insn)
-{
- insn_attr_t attr;
-
- attr = inat_get_opcode_attribute((insn_byte_t)*insn);
- while (inat_is_legacy_prefix(attr)) {
- insn++;
- attr = inat_get_opcode_attribute((insn_byte_t)*insn);
- }
-#ifdef CONFIG_X86_64
- if (inat_is_rex_prefix(attr))
- insn++;
-#endif
- return insn;
-}
-NOKPROBE_SYMBOL(skip_prefixes);
-
/*
* Returns non-zero if INSN is boostable.
* RIP relative instructions are adjusted at copying time in 64 bits mode
@@ -311,25 +291,6 @@ static int can_probe(unsigned long paddr)
return (addr == paddr);
}
-/*
- * Returns non-zero if opcode modifies the interrupt flag.
- */
-static int is_IF_modifier(kprobe_opcode_t *insn)
-{
- /* Skip prefixes */
- insn = skip_prefixes(insn);
-
- switch (*insn) {
- case 0xfa: /* cli */
- case 0xfb: /* sti */
- case 0xcf: /* iret/iretd */
- case 0x9d: /* popf/popfd */
- return 1;
- }
-
- return 0;
-}
-
/*
* Copy an instruction with recovering modified instruction by kprobes
* and adjust the displacement if the instruction uses the %rip-relative
@@ -411,9 +372,9 @@ static int prepare_boost(kprobe_opcode_t *buf, struct kprobe *p,
synthesize_reljump(buf + len, p->ainsn.insn + len,
p->addr + insn->length);
len += JMP32_INSN_SIZE;
- p->ainsn.boostable = true;
+ p->ainsn.boostable = 1;
} else {
- p->ainsn.boostable = false;
+ p->ainsn.boostable = 0;
}
return len;
@@ -450,12 +411,75 @@ void free_insn_page(void *page)
module_memfree(page);
}
+static void set_resume_flags(struct kprobe *p, struct insn *insn)
+{
+ insn_byte_t opcode = insn->opcode.bytes[0];
+
+ switch (opcode) {
+ case 0xfa: /* cli */
+ case 0xfb: /* sti */
+ case 0x9d: /* popf/popfd */
+ /* Check whether the instruction modifies Interrupt Flag or not */
+ p->ainsn.if_modifier = 1;
+ break;
+ case 0x9c: /* pushfl */
+ p->ainsn.is_pushf = 1;
+ break;
+ case 0xcf: /* iret */
+ p->ainsn.if_modifier = 1;
+ fallthrough;
+ case 0xc2: /* ret/lret */
+ case 0xc3:
+ case 0xca:
+ case 0xcb:
+ case 0xea: /* jmp absolute -- ip is correct */
+ /* ip is already adjusted, no more changes required */
+ p->ainsn.is_abs_ip = 1;
+ /* Without resume jump, this is boostable */
+ p->ainsn.boostable = 1;
+ break;
+ case 0xe8: /* call relative - Fix return addr */
+ p->ainsn.is_call = 1;
+ break;
+#ifdef CONFIG_X86_32
+ case 0x9a: /* call absolute -- same as call absolute, indirect */
+ p->ainsn.is_call = 1;
+ p->ainsn.is_abs_ip = 1;
+ break;
+#endif
+ case 0xff:
+ opcode = insn->opcode.bytes[1];
+ if ((opcode & 0x30) == 0x10) {
+ /*
+ * call absolute, indirect
+ * Fix return addr; ip is correct.
+ * But this is not boostable
+ */
+ p->ainsn.is_call = 1;
+ p->ainsn.is_abs_ip = 1;
+ break;
+ } else if (((opcode & 0x31) == 0x20) ||
+ ((opcode & 0x31) == 0x21)) {
+ /*
+ * jmp near and far, absolute indirect
+ * ip is correct.
+ */
+ p->ainsn.is_abs_ip = 1;
+ /* Without resume jump, this is boostable */
+ p->ainsn.boostable = 1;
+ }
+ break;
+ }
+}
+
static int arch_copy_kprobe(struct kprobe *p)
{
struct insn insn;
kprobe_opcode_t buf[MAX_INSN_SIZE];
int len;
+ memset(&p->ainsn, 0, sizeof(p->ainsn));
+
/* Copy an instruction with recovering if other optprobe modifies it.*/
len = __copy_instruction(buf, p->addr, p->ainsn.insn, &insn);
if (!len)
@@ -467,8 +491,8 @@ static int arch_copy_kprobe(struct kprobe *p)
*/
len = prepare_boost(buf, p, &insn);
- /* Check whether the instruction modifies Interrupt Flag or not */
- p->ainsn.if_modifier = is_IF_modifier(buf);
+ /* Analyze the opcode and set resume flags */
+ set_resume_flags(p, &insn);
/* Also, displacement change doesn't affect the first byte */
p->opcode = buf[0];
@@ -806,11 +830,6 @@ NOKPROBE_SYMBOL(trampoline_handler);
* 2) If the single-stepped instruction was a call, the return address
* that is atop the stack is the address following the copied instruction.
* We need to make it the address following the original instruction.
- *
- * If this is the first time we've single-stepped the instruction at
- * this probepoint, and the instruction is boostable, boost it: add a
- * jump instruction after the copied instruction, that jumps to the next
- * instruction after the probepoint.
*/
static void resume_execution(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb)
@@ -818,59 +837,20 @@ static void resume_execution(struct kprobe *p, struct pt_regs *regs,
unsigned long *tos = stack_addr(regs);
unsigned long copy_ip = (unsigned long)p->ainsn.insn;
unsigned long orig_ip = (unsigned long)p->addr;
- kprobe_opcode_t *insn = p->ainsn.insn;
-
- /* Skip prefixes */
- insn = skip_prefixes(insn);
regs->flags &= ~X86_EFLAGS_TF;
- switch (*insn) {
- case 0x9c: /* pushfl */
+
+ /* Fixup the contents of top of stack */
+ if (p->ainsn.is_pushf) {
*tos &= ~(X86_EFLAGS_TF | X86_EFLAGS_IF);
*tos |= kcb->kprobe_old_flags;
- break;
- case 0xc2: /* iret/ret/lret */
- case 0xc3:
- case 0xca:
- case 0xcb:
- case 0xcf:
- case 0xea: /* jmp absolute -- ip is correct */
- /* ip is already adjusted, no more changes required */
- p->ainsn.boostable = true;
- goto no_change;
- case 0xe8: /* call relative - Fix return addr */
+ } else if (p->ainsn.is_call) {
*tos = orig_ip + (*tos - copy_ip);
- break;
-#ifdef CONFIG_X86_32
- case 0x9a: /* call absolute -- same as call absolute, indirect */
- *tos = orig_ip + (*tos - copy_ip);
- goto no_change;
-#endif
- case 0xff:
- if ((insn[1] & 0x30) == 0x10) {
- /*
- * call absolute, indirect
- * Fix return addr; ip is correct.
- * But this is not boostable
- */
- *tos = orig_ip + (*tos - copy_ip);
- goto no_change;
- } else if (((insn[1] & 0x31) == 0x20) ||
- ((insn[1] & 0x31) == 0x21)) {
- /*
- * jmp near and far, absolute indirect
- * ip is correct. And this is boostable
- */
- p->ainsn.boostable = true;
- goto no_change;
- }
- default:
- break;
}
- regs->ip += orig_ip - copy_ip;
+ if (!p->ainsn.is_abs_ip)
+ regs->ip += orig_ip - copy_ip;
-no_change:
restore_btf();
}
NOKPROBE_SYMBOL(resume_execution);
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