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[2001:8b0:1d0::2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-427d68fa493sm138035665e9.10.2024.07.22.10.30.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jul 2024 10:30:00 -0700 (PDT) From: Peter Maydell To: qemu-arm@nongnu.org, qemu-devel@nongnu.org Cc: qemu-stable@nongnu.org Subject: [PATCH 3/4] target/arm: Avoid shifts by -1 in tszimm_shr() and tszimm_shl() Date: Mon, 22 Jul 2024 18:29:56 +0100 Message-Id: <20240722172957.1041231-4-peter.maydell@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240722172957.1041231-1-peter.maydell@linaro.org> References: <20240722172957.1041231-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::32a; envelope-from=peter.maydell@linaro.org; helo=mail-wm1-x32a.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: qemu-devel-bounces+patch=linaro.org@nongnu.org The function tszimm_esz() returns a shift amount, or possibly -1 in certain cases that correspond to unallocated encodings in the instruction set. We catch these later in the trans_ functions (generally with an "a-esz < 0" check), but before we do the decodetree-generated code will also call tszimm_shr() or tszimm_sl(), which will use the tszimm_esz() return value as a shift count without checking that it is not negative, which is undefined behaviour. Avoid the UB by checking the return value in tszimm_shr() and tszimm_shl(). Cc: qemu-stable@nongnu.org Resolves: Coverity CID 1547617, 1547694 Signed-off-by: Peter Maydell --- target/arm/tcg/translate-sve.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/target/arm/tcg/translate-sve.c b/target/arm/tcg/translate-sve.c index 798ab2bfb13..a72c2620960 100644 --- a/target/arm/tcg/translate-sve.c +++ b/target/arm/tcg/translate-sve.c @@ -50,13 +50,27 @@ static int tszimm_esz(DisasContext *s, int x) static int tszimm_shr(DisasContext *s, int x) { - return (16 << tszimm_esz(s, x)) - x; + /* + * We won't use the tszimm_shr() value if tszimm_esz() returns -1 (the + * trans function will check for esz < 0), so we can return any + * value we like from here in that case as long as we avoid UB. + */ + int esz = tszimm_esz(s, x); + if (esz < 0) { + return esz; + } + return (16 << esz) - x; } /* See e.g. LSL (immediate, predicated). */ static int tszimm_shl(DisasContext *s, int x) { - return x - (8 << tszimm_esz(s, x)); + /* As with tszimm_shr(), value will be unused if esz < 0 */ + int esz = tszimm_esz(s, x); + if (esz < 0) { + return esz; + } + return x - (8 << esz); } /* The SH bit is in bit 8. Extract the low 8 and shift. */