There are 2 bugs in the can_boost() function because of using
x86 insn decoder. Since the insn->opcode never has a prefix byte,
it can not find CS override prefix in it. And the insn->attr is
the attribute of the opcode, thus inat_is_address_size_prefix(
insn->attr) always returns false.
Fix those by checking each prefix bytes with for_each_insn_prefix
loop and getting the correct attribute for each prefix byte.
Also, this removes unlikely, because this is a slow path.
Fixes: a8d11cd0714f ("kprobes/x86: Consolidate insn decoder users for copying code")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
arch/x86/kernel/kprobes/core.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 89d9f26785c7..503958f15cf9 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -139,6 +139,8 @@ NOKPROBE_SYMBOL(synthesize_relcall);
int can_boost(struct insn *insn, void *addr)
{
kprobe_opcode_t opcode;
+ insn_byte_t prefix;
+ int i;
if (search_exception_tables((unsigned long)addr))
return 0; /* Page fault may occur on this address. */
@@ -151,9 +153,14 @@ int can_boost(struct insn *insn, void *addr)
if (insn->opcode.nbytes != 1)
return 0;
- /* Can't boost Address-size override prefix */
- if (unlikely(inat_is_address_size_prefix(insn->attr)))
- return 0;
+ for_each_insn_prefix(insn, i, prefix) {
+ insn_attr_t attr;
+
+ attr = inat_get_opcode_attribute(prefix);
+ /* Can't boost Address-size override prefix and CS override prefix */
+ if (prefix == 0x2e || inat_is_address_size_prefix(attr))
+ return 0;
+ }
opcode = insn->opcode.bytes[0];
@@ -181,8 +188,8 @@ int can_boost(struct insn *insn, void *addr)
/* indirect jmp is boostable */
return X86_MODRM_REG(insn->modrm.bytes[0]) == 4;
default:
- /* CS override prefix and call are not boostable */
- return (opcode != 0x2e && opcode != 0x9a);
+ /* call is not boostable */
+ return opcode != 0x9a;
}
}
