Messages in this thread | | | Date | Fri, 05 Oct 2007 09:55:05 +0900 | From | Shi Weihua <> | Subject | Re: [PATCH 1/3] signal(i386): alternative signal stack wraparound occurs |
| |
Mikael Pettersson wrote:: > On Thu, 4 Oct 2007 21:47:30 +0900, KAMEZAWA Hiroyuki wrote: >> On Thu, 04 Oct 2007 21:33:12 +0900 >> Shi Weihua <shiwh@cn.fujitsu.com> wrote: >> >>> KAMEZAWA Hiroyuki wrote:: >>>> On Thu, 04 Oct 2007 20:56:14 +0900 >>>> Shi Weihua <shiwh@cn.fujitsu.com> wrote: >>>> >>>>> stack.ss_sp = addr + pagesize; >>>>> stack.ss_flags = 0; >>>>> stack.ss_size = pagesize; >>>> Here is bad. >>>> stack,ss_sp = addr; >>>> stack.ss_flags = 0; >>>> stack.ss_size = pagesize * 2; >>> [What the test code want to do] >>> addr+pagesize*2 - addr+pagesize -> sigaltstack >>> addr+pagesize - addr -> protected region >>> The code want to catch overflow when esp enter the protected region. >>> >> You have to protect the top of *registered* sigaltstack. >> The reason of wraparound is %esp will be set to the bottom of sigaltstack >> if it is not on sigaltstack area when signaled. >> What you have to do is protect the top of registerd sigaltstack. >> If %esp is in the range of registerd sigaltstack at SEGV, wraparound >> will stop. > > Exactly right. You mprotect or munmap the end of the altstack, > not the area beyond it. So we tell users "Even if you protectted half of mmap's space, but you must to register all space to kernel. " ?
The image about my test code's result: No patch Patched ┌───────────┐ │ │← 1 ┌ ← 3 ← 1 │ A │ │(wraparound) │ │ │ │ │← 2 │ ← 2 │ │ │ ├───────────┤ │ │▒▒▒▒▒▒▒▒▒▒▒│← 3 ┘ ← 3 │▒▒▒▒B▒▒▒▒▒▒│ (caught) │▒protected▒│ │▒▒▒▒▒▒▒▒▒▒▒│ │▒▒▒▒▒▒▒▒▒▒▒│ └───────────┘ A+B mmap's space A sigaltstack B protectted
I agree that if register A+B to kernel, the wraparound will stop. But if register A to kernel, why not kernel do something?
Thanks Shi Weihua > > /Mikael > > >
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |