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Sachin Monga
e622f82ea8
The Power8 strncasecmp (strcasecmp.S with USE_AS_STRNCASECMP) touches s1[n]/s2[n] in three places when the first n bytes compare equal and contain no NUL: L(loop) preloads the next byte before its bdnz; L(loop1) increments then loads before its bdnz; and L(bytebybyte) loads s1[0]/s2[0] before checking r5. A caller that maps exactly n readable bytes can get SIGSEGV if byte n falls on an unmapped page. The L(bytebybyte) site was identified by Florian Weimer; the original AISLE report covered only the two loops. Fix all three sites: guard L(bytebybyte) with a r5 == 0 check, split the bdnz/load pairs in L(loop) and L(loop1) so the load only runs when the count is still positive, and preload rCHAR1/rCHAR2 in L(lessthan4) after confirming r5 != 0. strcasecmp is unaffected; its generated code is unchanged. Add string/test-strncasecmp-nonarray.c, built on the test-Xncmp-nonarray.c skeleton: maps a PROT_NONE page past both buffers and sweeps all start offsets and lengths. Runs as an xtest. Reported-by: AISLE in partnership with Red Hat Suggested-by: Florian Weimer <fweimer@redhat.com>
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