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[76.191.17.161]) by smtp.googlemail.com with ESMTPSA id n23sm23001491ioo.55.2022.02.15.08.28.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Feb 2022 08:28:34 -0800 (PST) To: libc-alpha@sourceware.org Subject: [PATCH v1] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895] Date: Tue, 15 Feb 2022 10:28:29 -0600 Message-Id: <20220215162829.282223-1-goldstein.w.n@gmail.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 X-Spam-Status: No, score=-12.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Noah Goldstein via Libc-alpha From: Noah Goldstein Reply-To: Noah Goldstein Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" Logic can read before the start of `s1` / `s2` if both `s1` and `s2` are near the start of a page. To avoid having the result contimated by these comparisons the `strcmp` variants would mask off these comparisons. This was missing in the `strncmp` variants causing the bug. This commit adds the masking to `strncmp` so that out of range comparisons don't affect the result. test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as well a full xcheck on x86_64 linux. --- string/test-strncmp.c | 24 ++++++++++++++++++++++++ sysdeps/x86_64/multiarch/strcmp-avx2.S | 1 + sysdeps/x86_64/multiarch/strcmp-evex.S | 1 + 3 files changed, 26 insertions(+) diff --git a/string/test-strncmp.c b/string/test-strncmp.c index 831cb77893..501055de0c 100644 --- a/string/test-strncmp.c +++ b/string/test-strncmp.c @@ -423,6 +423,29 @@ check3 (void) } } + +static void +check4 (void) +{ + /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of + the end of the page. 2) For there to be no mismatch/null byte before the + first page cross. 3) For length (`n`) to be large enough for one string to + cross the page. And 4) for there to be either mismatch/null bytes before + the start of the strings. */ + + size_t size = 10; + CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR)); + CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR)); + int exp_result; + + STRCPY (s1, L ("tst-tlsmod%")); + STRCPY (s2, L ("tst-tls-manydynamic73mod")); + exp_result = SIMPLE_STRNCMP (s1, s2, size); + FOR_EACH_IMPL (impl, 0) + check_result (impl, s1, s2, size, exp_result); +} + + static void check_overflow (void) { @@ -546,6 +569,7 @@ test_main (void) check1 (); check2 (); check3 (); + check4 (); printf ("%23s", ""); FOR_EACH_IMPL (impl, 0) diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S index 99e5349be8..07a5a2c889 100644 --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S @@ -661,6 +661,7 @@ L(ret8): # ifdef USE_AS_STRNCMP .p2align 4,, 10 L(return_page_cross_end_check): + andl %r10d, %ecx tzcntl %ecx, %ecx leal -VEC_SIZE(%rax, %rcx), %ecx cmpl %ecx, %edx diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S index 6f42e3155a..56d8c118e4 100644 --- a/sysdeps/x86_64/multiarch/strcmp-evex.S +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S @@ -689,6 +689,7 @@ L(ret8): # ifdef USE_AS_STRNCMP .p2align 4,, 10 L(return_page_cross_end_check): + andl %r10d, %ecx tzcntl %ecx, %ecx leal -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx # ifdef USE_AS_WCSCMP