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libthr: work around an ASAN false-positive

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I got the following error with an ASAN-instrument libthr:

==803==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fffffffcdb0 at pc 0x000801863396 bp 0x7ff8
READ of size 4 at 0x7fffffffcdb0 thread T0
    #0 0x801863395 in handle_signal /local/scratch/alr48/cheri/freebsd/lib/libthr/thread/thr_sig.c:262:2
    #1 0x801860da2 in thr_sighandler /local/scratch/alr48/cheri/freebsd/lib/libthr/thread/thr_sig.c:246:2

Address 0x7fffffffcdb0 is located in stack of thread T0 at offset 208 in frame
    #0 0x80186080f in thr_sighandler /local/scratch/alr48/cheri/freebsd/lib/libthr/thread/thr_sig.c:213

  This frame has 1 object(s):
    [32, 64) 'act' (line 216) <== Memory access at offset 208 overflows this variable
HINT: this may be a false positive if your program uses some custom stack

This seems like a false-positive since the line in question is
`SIGSETOR(actp->sa_mask, ucp->uc_sigmask);` and it complains about a read
operation (from the ucontext_t argument) so this indicates to me that ASAN
does not understand that thr_sighandler() is a signal handler.

Differential Revision: https://reviews.freebsd.org/D31074
This commit is contained in:
Alex Richardson 2021-08-02 09:49:21 +01:00
parent 7bc797e3f3
commit 9efbe526e0
1 changed files with 6 additions and 0 deletions
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6
lib/libthr/Makefile
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@ -29,6 +29,12 @@ CFLAGS+=-I${SRCTOP}/lib/libthread_db
CFLAGS.thr_stack.c+= -Wno-cast-align
CFLAGS.rtld_malloc.c+= -Wno-cast-align
CFLAGS.thr_symbols.c+= -Wno-missing-variable-declarations
.if ${MK_ASAN} != "no"
# False-positive ASAN error claiming the local "struct sigaction act;" is
# overflowed by handle_signal() reading from the ucontext_t argument. This
# could be caused by ASAN not treating this function as a signal handler.
CFLAGS.thr_sig.c+= -fno-sanitize=address
.endif
.ifndef NO_THREAD_UNWIND_STACK
CFLAGS+=-fexceptions