Commit 91e5ed49fca0 ("x86/asm/decoder: Fix and enforce max instruction
size in the insn decoder") has changed MAX_INSN_SIZE from 16 to 15 bytes
on x86.
As a side effect, the slots Kprobes use to store the instructions became
1 byte shorter. This is unfortunate because, for example, the Kprobes'
"boost" feature can not be used now for the instructions of length 11,
like a quite common kind of MOV:
* movq $0xffffffffffffffff,-0x3fe8(%rax) (48 c7 80 18 c0 ff ff ff ff ff ff)
* movq $0x0,0x88(%rdi) (48 c7 87 88 00 00 00 00 00 00 00)
and so on.
This patch makes the insn slots 16 bytes long, like they were before while
keeping MAX_INSN_SIZE intact.
Other tools may benefit from this change as well.
Signed-off-by: Eugene Shatokhin <eugene.shatok...@rosalab.ru>
---
arch/x86/include/asm/kprobes.h | 1 +
arch/x86/kernel/kprobes/core.c | 2 +-
kernel/kprobes.c | 8 ++++++--
3 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 4421b5d..f3f0b4e 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -27,6 +27,7 @@
#include <asm/insn.h>
#define __ARCH_WANT_KPROBES_INSN_SLOT
+#define KPROBE_INSN_SLOT_SIZE 16
struct pt_regs;
struct kprobe;
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 0a42b76..1067f90 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -881,7 +881,7 @@ static void resume_execution(struct kprobe *p, struct
pt_regs *regs,
if (p->ainsn.boostable == 0) {
if ((regs->ip > copy_ip) &&
- (regs->ip - copy_ip) + 5 <= MAX_INSN_SIZE) {
+ (regs->ip - copy_ip) + 5 <= KPROBE_INSN_SLOT_SIZE) {
/*
* These instructions can be executed directly if it
* jumps back to correct address.
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c90e417..1dc074d 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -57,7 +57,6 @@
#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)
-
/*
* Some oddball architectures like 64bit powerpc have function descriptors
* so this must be overridable.
@@ -90,6 +89,11 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned
long hash)
static LIST_HEAD(kprobe_blacklist);
#ifdef __ARCH_WANT_KPROBES_INSN_SLOT
+
+#ifndef KPROBE_INSN_SLOT_SIZE
+#define KPROBE_INSN_SLOT_SIZE MAX_INSN_SIZE
+#endif
+
/*
* kprobe->ainsn.insn points to the copy of the instruction to be
* single-stepped. x86_64, POWER4 and above have no-exec support and
@@ -135,7 +139,7 @@ struct kprobe_insn_cache kprobe_insn_slots = {
.alloc = alloc_insn_page,
.free = free_insn_page,
.pages = LIST_HEAD_INIT(kprobe_insn_slots.pages),
- .insn_size = MAX_INSN_SIZE,
+ .insn_size = KPROBE_INSN_SLOT_SIZE,
.nr_garbage = 0,
};
static int collect_garbage_slots(struct kprobe_insn_cache *c);
--
2.3.2
--
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