Re: [bug?] Access was denied by memory protection keys in execute-only address

[Li Wang <liwang@redhat.com>]

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On Fri, Mar 9, 2018 at 12:45 AM, Ram Pai <linuxram@us.ibm.com> wrote:

> On Thu, Mar 08, 2018 at 11:19:12PM +1100, Michael Ellerman wrote:
> > Li Wang <liwang@redhat.com> writes:
> > > Hi,
> > >
> > > ltp/mprotect04[1] crashed by SEGV_PKUERR on ppc64(LPAR on P730, Power 8
> > > 8247-22L) with kernel-v4.16.0-rc4.
> > >
> > > 10000000-10020000 r-xp 00000000 fd:00 167223           mprotect04
> > > 10020000-10030000 r--p 00010000 fd:00 167223           mprotect04
> > > 10030000-10040000 rw-p 00020000 fd:00 167223           mprotect04
> > > 1001a380000-1001a3b0000 rw-p 00000000 00:00 0          [heap]
> > > 7fffa6c60000-7fffa6c80000 --xp 00000000 00:00 0 ​
> > >
> > > ​&exec_func = 0x10030170​
> > >
> > > ​&func = 0x7fffa6c60170​
> > >
> > > ​While perform ​
> > > "(*func)();" we get the
> > > ​segmentation fault.
> > > ​
> > >
> > > ​strace log:​
> > >
> > > -------------------
> > > ​mprotect(0x7fffaed00000, 131072, PROT_EXEC) = 0
> > > rt_sigprocmask(SIG_BLOCK, NULL, [], 8)  = 0
> > > --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_PKUERR,
> si_addr=0x7fffaed00170}
> > > ---​
> >
> > Looks like a bug to me.
> >
> > Please Cc linuxppc-dev on powerpc bugs.
> >
> > I also can't reproduce this failure on my machine.
> > Not sure what's going on?
>
> I could reproduce it on a power7 lpar.  But not on a power8 lpar.
>
> The problem seems to be that the cpu generates a key exception if
> the page with Read/Write-disable-but-execute-enable key is executed
> on power7. If I enable read on that key, the exception disappears.
>

After adding read permission on that key, reproducer get PASS on my power8
machine too.​
​(​mprotect(..,PROT_READ | PROT_EXEC))​



>
> BTW: the testcase executes
> ​​
> mprotect(..,PROT_EXEC).
> The mprotect(, PROT_EXEC) system call internally generates a
> execute-only key and associates it with the pages in the address-range.


> Now since Li Wang claims that he can reproduce it on power8 as well, i
> am wondering if the slightly different cpu behavior is dependent on the
> version of the firmware/microcode?
>

​I also run this reproducer on series ppc kvm machines, but none of them
get the FAIL.
If you need some more HW info, pls let me know.​



>
>
> RP
>
>


-- 
Li Wang
liwang@redhat.com

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