executor: fix cover_protect() on FreeBSD #5799
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a-nogikh
reviewed
Feb 19, 2025
During machine checks, syzkaller will execute calls with coverage disabled, in which case per-thread coverage structures are zeroed out. write_output() will temporarily map the coverage data as writeable via CoverAccessScope, whether or not cover is enabled. In effect, write_output() may trigger a call mprotect(0, kCoverSize, PROT_RW). On FreeBSD, mprotect() silently ignores unmapped regions, so this does not result in an error. In fact, kCoverSize is now large enough that this ends up removing the eXecute bit from part of syz-executor's text region. Make CoverAccessScope a no-op if coverage is not enabled. Modify BSD cover_protect() and cover_unprotect() to fail if invoked when coverage is disabled.
a-nogikh
approved these changes
Feb 21, 2025
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I think the OpenBSD version has the same problem, but didn't want to modify it as I'm not set up to test. Perhaps @blackgnezdo can confirm?