On Fri, Mar 09, 2018 at 11:43:00AM +0800, Li Wang wrote:
> On Fri, Mar 9, 2018 at 12:45 AM, Ram Pai <[1]linuxram@xxxxxxxxxx> wrote:
>
> On Thu, Mar 08, 2018 at 11:19:12PM +1100, Michael Ellerman wrote:
> > Li Wang <[2]liwang@xxxxxxxxxx> 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.
Hi Li,
Can you try the following patch and see if it solves your problem.
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index c269817..184a10a 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/arch/powerpc/mm/pkeys.c
@@ -421,7 +421,7 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
* The requested protection is execute-only. Hence let's use an
* execute-only pkey.
*/
- if (prot == PROT_EXEC) {
+ if (prot == PROT_EXEC && pkey_execute_disable_supported) {
pkey = execute_only_pkey(vma->vm_mm);
if (pkey > 0)
return pkey;
Thanks
RP
