On Thu, Mar 7, 2019 at 12:22 AM Tong Bo <bo.tong@xxxxxxxxx> wrote: > > Atom-based CPUs trigger stack fault when invoke 32-bit SYSENTER instruction > with invalid register values. So we also need sigbus handling in this case. > > Following is assembly when the fault expception happens. > > (gdb) disassemble $eip > Dump of assembler code for function __kernel_vsyscall: > 0xf7fd8fe0 <+0>: push %ecx > 0xf7fd8fe1 <+1>: push %edx > 0xf7fd8fe2 <+2>: push %ebp > 0xf7fd8fe3 <+3>: mov %esp,%ebp > 0xf7fd8fe5 <+5>: sysenter > 0xf7fd8fe7 <+7>: int $0x80 > => 0xf7fd8fe9 <+9>: pop %ebp > 0xf7fd8fea <+10>: pop %edx > 0xf7fd8feb <+11>: pop %ecx > 0xf7fd8fec <+12>: ret > End of assembler dump. > > Accroding to Intel SDM, this could also be a Stack Segment Fault(#SS, 12), > except a normal Page Fault(#PF, 14). Really? What is in the SS register that makes a stack segment fault possible? Is it because we're overflowing ESP? Would a value like -5 instead of -1 in the register change things? Anyway, I'm okay with the patch, but I think that you should improve the comment: > - sethandler(SIGSEGV, sigsegv, SA_ONSTACK); > + sethandler(SIGSEGV, sigsegv_or_sigbus, SA_ONSTACK); > + /* Atom CPUs may trigger sigbus for below SYSENTER exception case */ > + sethandler(SIGBUS, sigsegv_or_sigbus, SA_ONSTACK); How about "The actual exception can vary. On Atom CPUs, we get #SS instead of #PF when the vDSO fails to access the stack when ESP is too close to 2^32, and #SS causes SIGBUS". --Andy
