Message ID | 56A25783.7040502@linux.vnet.ibm.com (mailing list archive) |
---|---|
State | Changes Requested |
Headers | show |
Hi Gustavo, On Fri, 2016-22-01 at 16:23:31 UTC, Gustavo Romero wrote: > Fix si->si_code for guard page access on PowerPC > ... > > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index a67c6d7..6954971 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -431,8 +431,10 @@ good_area: > */ > fault = handle_mm_fault(mm, vma, address, flags); > if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) { > - if (fault & VM_FAULT_SIGSEGV) > + if (fault & VM_FAULT_SIGSEGV) { > + code = SEGV_MAPERR; > goto bad_area; > + } > rc = mm_fault_error(regs, address, fault); > if (rc >= MM_FAULT_RETURN) > goto bail; As we discussed on IRC, I'd prefer if this case was handled in mm_fault_error(). So please send a v2 which does that, or let us know if you have problems. cheers
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c index a67c6d7..6954971 100644 --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -431,8 +431,10 @@ good_area: */ fault = handle_mm_fault(mm, vma, address, flags); if (unlikely(fault & (VM_FAULT_RETRY|VM_FAULT_ERROR))) { - if (fault & VM_FAULT_SIGSEGV) + if (fault & VM_FAULT_SIGSEGV) { + code = SEGV_MAPERR; goto bad_area; + } rc = mm_fault_error(regs, address, fault); if (rc >= MM_FAULT_RETURN) goto bail;
Fix si->si_code for guard page access on PowerPC Currently, the mm code on PowerPC/POWER returns a si->si_code = 2 (SEGV_ACCERR) when the stack tries to grow beyond the stack guard (stack ulimit). On other architectures, notably x86, the si->si_code returned when a guard page access occurs is 1 (SEGV_MAPERR). Although si->si_code is not historically reliable and hence no program should trust it for any semantic behavior, the right si->si_code for a guard page access is 1 (SEGV_MAPERR) and, besides that, some tests still trust it in specific cases. On PowerPC/POWER, if the mm tries to expand the stack and hits a page mapped by the program (say, an anonymous page with permission ---p) it generates a SIG_SEGV and a si->si_code = 2 (SEGV_ACCERR), the same way it happens on x86. But then, when this guard page is removed (un-mapped) and the stack grows again reaching the stack guard (stack ulimit), the mm generates a SIG_SEGV and a si->si_code = 2 (SEGV_ACCERR) again, contrary to, for example, what happens on x86 (si->si_code = 1 (SIG_MAPERR)). It means that on PowerPC/POWER there is no semantic difference between a stack growth hitting a mapped area the stack has no permission to rd/wr and reaching the stack limit (stack ulimit), although indeed there is a difference. Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com> --- arch/powerpc/mm/fault.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)