Hi Michael, Unfortunately, this patch doesn't completely solve the problem.
Trying the original reproducer, I'm still able to trigger the crash even with this patch, although not 100% of the time. (If I turn ASLR off outside of tmux it reliably crashes, if I turn ASLR off _inside_ of tmux it reliably succeeds; all of this is on a serial console.) ./foo 1241000 & sleep 1; killall -USR1 foo; echo ok If I add some debugging information, I see that I'm getting address + 4096 = 7fffffed0fa0 gpr1 = 7fffffed1020 So address + 4096 is 0x80 bytes below the 4k window. I haven't been able to figure out why, gdb gives me a NIP in __kernel_sigtramp_rt64 but I don't know what to make of that. Kind regards, Daniel P.S. I don't know what your policy on linking to kernel bugzilla is, but if you want: Link: https://bugzilla.kernel.org/show_bug.cgi?id=205183 > Reported-by: Tom Lane <t...@sss.pgh.pa.us> > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > --- > arch/powerpc/mm/fault.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c > index 641fc5f3d7dd..ed01329dd12b 100644 > --- a/arch/powerpc/mm/fault.c > +++ b/arch/powerpc/mm/fault.c > @@ -274,7 +274,7 @@ static bool bad_stack_expansion(struct pt_regs *regs, > unsigned long address, > /* > * N.B. The POWER/Open ABI allows programs to access up to > * 288 bytes below the stack pointer. > - * The kernel signal delivery code writes up to about 1.5kB > + * The kernel signal delivery code writes up to 4KB > * below the stack pointer (r1) before decrementing it. > * The exec code can write slightly over 640kB to the stack > * before setting the user r1. Thus we allow the stack to > @@ -299,7 +299,7 @@ static bool bad_stack_expansion(struct pt_regs *regs, > unsigned long address, > * between the last mapped region and the stack will > * expand the stack rather than segfaulting. > */ > - if (address + 2048 >= uregs->gpr[1]) > + if (address + 4096 >= uregs->gpr[1]) > return false; > > if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) && > -- > 2.25.1
