[PATCH 5.14 35/48] x86/insn, tools/x86: Fix undefined behavior due to potential unaligned accesses

Greg Kroah-Hartman
2021-10-08T11:40:41Z

From: Numfor Mbiziwo-Tiapo <nums@google.com>

[ Upstream commit 5ba1071f7554c4027bdbd712a146111de57918de ]

Don't perform unaligned loads in __get_next() and __peek_nbyte_next() as
these are forms of undefined behavior:

"A pointer to an object or incomplete type may be converted to a pointer
to a different object or incomplete type. If the resulting pointer
is not correctly aligned for the pointed-to type, the behavior is
undefined."

(from http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf)

These problems were identified using the undefined behavior sanitizer
(ubsan) with the tools version of the code and perf test.

[ bp: Massage commit message. ]

Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lkml.kernel.org/r/20210923161843.751834-1-irogers@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/lib/insn.c | 4 ++--
tools/arch/x86/lib/insn.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 058f19b20465..c565def611e2 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -37,10 +37,10 @@
((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)

#define __get_next(t, insn) \
- ({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); leXX_to_cpu(t, r); })
+ ({ t r; memcpy(&r, insn->next_byte, sizeof(t)); insn->next_byte += sizeof(t); leXX_to_cpu(t, r); })

#define __peek_nbyte_next(t, insn, n) \
- ({ t r = *(t*)((insn)->next_byte + n); leXX_to_cpu(t, r); })
+ ({ t r; memcpy(&r, (insn)->next_byte + n, sizeof(t)); leXX_to_cpu(t, r); })

#define get_next(t, insn) \
({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
index c41f95815480..797699462cd8 100644
--- a/tools/arch/x86/lib/insn.c
+++ b/tools/arch/x86/lib/insn.c
@@ -37,10 +37,10 @@
((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)

#define __get_next(t, insn) \
- ({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); leXX_to_cpu(t, r); })
+ ({ t r; memcpy(&r, insn->next_byte, sizeof(t)); insn->next_byte += sizeof(t); leXX_to_cpu(t, r); })

#define __peek_nbyte_next(t, insn, n) \
- ({ t r = *(t*)((insn)->next_byte + n); leXX_to_cpu(t, r); })
+ ({ t r; memcpy(&r, (insn)->next_byte + n, sizeof(t)); leXX_to_cpu(t, r); })

#define get_next(t, insn) \
({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
--
2.33.0