linux-kernel - [PATCH 2/2] tools/x86: Fix some potential undefined behavior

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Message-Id: <20201015062148.1437894-2-irogers@google.com>
Date:   Wed, 14 Oct 2020 23:21:48 -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 2/2] tools/x86: 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  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>
---
 tools/arch/x86/lib/insn.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/arch/x86/lib/insn.c b/tools/arch/x86/lib/insn.c
index 0151dfc6da61..e8874a8cac2c 100644
--- a/tools/arch/x86/lib/insn.c
+++ b/tools/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