Re: linux-next: Unable to write into a vma if it has been mapped without PROT_READ
From: Kirill A. Shutemov <hidden>
Date: 2016-02-29 20:16:02
Also in:
linux-next
On Mon, Feb 29, 2016 at 11:11:37AM -0800, Andrey Wagin wrote:
quoted hunk ↗ jump to hunk
Hello Everyone, I found that now we can't write into a vma if it was mapped without PROT_READ: mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2ac7eb8000--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR, si_addr=0x7f2ac7eb8000} --- +++ killed by SIGSEGV (core dumped) +++Segmentation fault [root@linux-next-test ~]# cat test.c #include <sys/mman.h> #include <stdlib.h> int main() { int *p; p = mmap(NULL, 4096, PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); p[0] = 1; return 0; } [root@linux-next-test ~]# uname -a Linux linux-next-test 4.5.0-rc6-next-20160229 #1 SMP Mon Feb 29 17:38:25 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux This issue appeared in 4.5.0-rc5-next-20160226. https://ci.openvz.org/job/CRIU-linux-next/152/console
Looks like the regression is caused by change in access_error() by commit
62b5f7d013fc ("mm/core, x86/mm/pkeys: Add execute-only protection keys support")
as per next-20160229.
/*
* Assume all accesses require either read or execute
* permissions. This is not an instruction access, so
* it requires read permissions.
*/
if (!(vma->vm_flags & VM_READ))
return 1;
The assumption is false, taking this testcase into account.
Dave?
--
Kirill A. Shutemov
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