From: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
[ Upstream commit 91e5ed49fca09c2b83b262b9757d1376ee2b46c3 ]
x86 instructions cannot exceed 15 bytes, and the instruction
decoder should enforce that. Prior to 6ba48ff46f76, the
instruction length limit was implicitly set to 16, which was an
approximation of 15, but there is currently no limit at all.
Fix MAX_INSN_SIZE (it should be 15, not 16), and fix the decoder
to reject instructions that exceed MAX_INSN_SIZE.
Other than potentially confusing some of the decoder sanity
checks, I'm not aware of any actual problems that omitting this
check would cause, nor am I aware of any practical problems
caused by the MAX_INSN_SIZE error.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Fixes: 6ba48ff46f76 ("x86: Remove arbitrary instruction size limit ...
Link: http://lkml.kernel.org/r/f8f0bc9b8c58cfd6830f7d88400bf1396cbdcd0f.1422403511.git.luto@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
---
arch/x86/include/asm/insn.h | 2 +-
arch/x86/lib/insn.c | 7 +++++++
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
index 48eb30a..3eabe5c 100644
--- a/arch/x86/include/asm/insn.h
+++ b/arch/x86/include/asm/insn.h
@@ -68,7 +68,7 @@ struct insn {
const insn_byte_t *next_byte;
};
-#define MAX_INSN_SIZE 16
+#define MAX_INSN_SIZE 15
#define X86_MODRM_MOD(modrm) (((modrm) & 0xc0) >> 6)
#define X86_MODRM_REG(modrm) (((modrm) & 0x38) >> 3)
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 54fcffe..d979c5b 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -52,6 +52,13 @@
*/
void insn_init(struct insn *insn, const void *kaddr, int x86_64)
{
+ /*
+ * Instructions longer than MAX_INSN_SIZE (15 bytes) are invalid
+ * even if the input buffer is long enough to hold them.
+ */
+ if (buf_len > MAX_INSN_SIZE)
+ buf_len = MAX_INSN_SIZE;
+
memset(insn, 0, sizeof(*insn));
insn->kaddr = kaddr;
insn->next_byte = kaddr;
--
2.1.0
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