linux-kernel - [PATCH 1/2] x86/insn: Fix some potential undefined behavior.

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Message-Id: <20201015062148.1437894-1-irogers@google.com>
Date:   Wed, 14 Oct 2020 23:21:47 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Numfor Mbiziwo-Tiapo <nums@...gle.com>,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH 1/2] x86/insn: Fix some potential undefined behavior.

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

If insn_init is given a NULL kaddr and 0 buflen then validate_next will
perform arithmetic on NULL, add a guard to avoid this.

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

These problems were identified using the undefined behavior sanitizer
(ubsan) with the tools version of the code and perf test. Part of this
patch was previously posted here:
https://lore.kernel.org/lkml/20190724184512.162887-4-nums@google.com/

Signed-off-by: Ian Rogers <irogers@...gle.com>
Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
---
 arch/x86/lib/insn.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 404279563891..57236940de46 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -17,13 +17,13 @@
 
 /* Verify next sizeof(t) bytes can be on the same instruction */
 #define validate_next(t, insn, n)	\
-	((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
+	((insn)->end_kaddr != 0 && (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); r; })
+	({ t r; memcpy(&r, insn->next_byte, sizeof(t)); insn->next_byte += sizeof(t); r; })
 
 #define __peek_nbyte_next(t, insn, n)	\
-	({ t r = *(t*)((insn)->next_byte + n); r; })
+	({ t r; memcpy(&r, (insn)->next_byte + n, sizeof(t)); r; })
 
 #define get_next(t, insn)	\
 	({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
-- 
2.28.0.1011.ga647a8990f-goog