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From: Noah Goldstein <nwg@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] x86: Fix strncat-avx2.S reading past length [BZ #30065] Date: Wed, 1 Feb 2023 01:14:11 +0000 (GMT) [thread overview] Message-ID: <20230201011411.C51723858D38@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2c474f8de4c92bfe7435853a96805ec32d68dfa commit b2c474f8de4c92bfe7435853a96805ec32d68dfa Author: Noah Goldstein <goldstein.w.n@gmail.com> Date: Tue Jan 31 17:46:56 2023 -0600 x86: Fix strncat-avx2.S reading past length [BZ #30065] Occurs when `src` has no null-term. Two cases: 1) Zero-length check is doing: ``` test %rdx, %rdx jl L(zero_len) ``` which doesn't actually check zero (was at some point `decq` and the flag never got updated). The fix is just make the flag `jle` i.e: ``` test %rdx, %rdx jle L(zero_len) ``` 2) Length check in page-cross case checking if we should continue is doing: ``` cmpq %r8, %rdx jb L(page_cross_small) ``` which means we will continue searching for null-term if length ends at the end of a page and there was no null-term in `src`. The fix is to make the flag: ``` cmpq %r8, %rdx jbe L(page_cross_small) ``` Diff: --- string/test-strncat.c | 25 ++++++++++++++++++++++++- sysdeps/x86_64/multiarch/strncat-avx2.S | 4 ++-- 2 files changed, 26 insertions(+), 3 deletions(-) diff --git a/string/test-strncat.c b/string/test-strncat.c index e03d329e1c..c0cde206ee 100644 --- a/string/test-strncat.c +++ b/string/test-strncat.c @@ -28,6 +28,7 @@ # define CHAR char # define UCHAR unsigned char # define SIMPLE_STRNCAT simple_strncat +# define STRNLEN strnlen # define STRLEN strlen # define MEMSET memset # define MEMCPY memcpy @@ -40,6 +41,7 @@ # define CHAR wchar_t # define UCHAR wchar_t # define SIMPLE_STRNCAT simple_wcsncat +# define STRNLEN wcsnlen # define STRLEN wcslen # define MEMSET wmemset # define MEMCPY wmemcpy @@ -78,7 +80,7 @@ do_one_test (impl_t *impl, CHAR *dst, const CHAR *src, size_t n) return; } - size_t len = STRLEN (src); + size_t len = STRNLEN (src, n); if (MEMCMP (dst + k, src, len + 1 > n ? n : len + 1) != 0) { error (0, 0, "Incorrect concatenation in function %s", @@ -95,6 +97,26 @@ do_one_test (impl_t *impl, CHAR *dst, const CHAR *src, size_t n) } } +static void +do_test_src_no_nullterm_bz30065 (void) +{ + /* NB: "src does not need to be null-terminated if it contains n or more + * bytes." */ + CHAR *s1, *s2; + size_t bound = page_size / sizeof (CHAR); + s1 = (CHAR *) (buf1 + BUF1PAGES * page_size); + s2 = (CHAR *) buf2; + MEMSET (s1 - bound, -1, bound); + for (size_t n = 0; n < bound; ++n) + { + FOR_EACH_IMPL (impl, 0) + { + s2[0] = '\0'; + do_one_test (impl, s2, s1 - n, n); + } + } +} + static void do_test (size_t align1, size_t align2, size_t len1, size_t len2, size_t n, int max_char) @@ -372,6 +394,7 @@ test_main (void) do_random_tests (); do_overflow_tests (); + do_test_src_no_nullterm_bz30065 (); return ret; } diff --git a/sysdeps/x86_64/multiarch/strncat-avx2.S b/sysdeps/x86_64/multiarch/strncat-avx2.S index b380e8e11c..c2ff202238 100644 --- a/sysdeps/x86_64/multiarch/strncat-avx2.S +++ b/sysdeps/x86_64/multiarch/strncat-avx2.S @@ -66,7 +66,7 @@ ENTRY(STRNCAT) salq $2, %rdx # else test %rdx, %rdx - jl L(zero_len) + jle L(zero_len) # endif vpxor %VZERO_128, %VZERO_128, %VZERO_128 @@ -387,7 +387,7 @@ L(page_cross): subl %esi, %r8d andl $(VEC_SIZE - 1), %r8d cmpq %r8, %rdx - jb L(page_cross_small) + jbe L(page_cross_small) /* Optimizing more aggressively for space as this is very cold code. This saves 2x cache lines. */
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