Messages in this thread | | | Date | Tue, 14 Oct 2003 15:28:55 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: [x86] Access off the bottom of stack causes a segfault? |
| |
On Tue, 14 Oct 2003, Chris Lattner wrote:
> > > Generated code: > > > .intel_syntax > > > ... > > > main: > > > mov DWORD PTR [%ESP - 16004], %EBP # Save EBP to stack > > ^^^^^^^^^^^^ > > > > Yes, this is the problem (even Windows does that IIRC). > > Ok, I realize what's going on here. The question is, why does the linux > kernel consider this to be a bug? Where (in the X86 specs) is it > documented that it's illegal to access off the bottom of the stack? > > My compiler does a nice leaf function optimization where it does not even > bother to adjust the stack for leaf functions, which eliminates the adds > and subtracts entirely from these (common) functions. This completely > invalidates the optimization. > > Since I'm going to have to live with lots of preexisting kernels, it looks > like I'm going to have to disable it entirely, which is disappointing. > I'm still curious though why this is thought to be illegal. > > -Chris
Any interrupt causes the return address to be pushed onto the stack. This will overwrite any data you've put there. In principle, in user-mode, you can write below the stack-pointer because an interrupt uses the kernel stack. However, your data will still get corrupted by signal delivery, etc. So as to not corrupt your user-mode stack, the kernel calls your signal code, just like a nested call. This means the new return address will be below the non-signal user-mode stack-pointer value. This will surely corrupt anything you have written below the stack-pointer.
Cheers, Dick Johnson Penguin : Linux version 2.4.22 on an i686 machine (797.90 BogoMips). Note 96.31% of all statistics are fiction.
- 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/
| |