linux-kernel - [tip: x86/urgent] x86/insn, tools/x86: Fix undefined behavior due to potential unaligned accesses

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Date:   Fri, 24 Sep 2021 10:45:18 -0000
From:   "tip-bot2 for Numfor Mbiziwo-Tiapo" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Numfor Mbiziwo-Tiapo" <nums@...gle.com>,
        Ian Rogers <irogers@...gle.com>, Borislav Petkov <bp@...e.de>,
        Masami Hiramatsu <mhiramat@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/insn, tools/x86: Fix undefined behavior due to
 potential unaligned accesses

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     5ba1071f7554c4027bdbd712a146111de57918de
Gitweb:        https://git.kernel.org/tip/5ba1071f7554c4027bdbd712a146111de57918de
Author:        Numfor Mbiziwo-Tiapo <nums@...gle.com>
AuthorDate:    Thu, 23 Sep 2021 09:18:43 -07:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Fri, 24 Sep 2021 12:37:38 +02:00

x86/insn, tools/x86: Fix undefined behavior due to potential unaligned accesses

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@...gle.com>
Signed-off-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Link: https://lkml.kernel.org/r/20210923161843.751834-1-irogers@google.com
---
 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 058f19b..c565def 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 c41f958..7976994 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); })