On Mon, Feb 29, 2016 at 11:11:37AM -0800, Andrey Wagin wrote:
> 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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