Re: [PATCH v7 5/6] x86/signal: Detect and prevent an alternate signal stack overflow

[Borislav Petkov]

On Mon, Mar 15, 2021 at 11:52:14PM -0700, Chang S. Bae wrote:
> @@ -272,7 +275,8 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, size_t frame_size,
>  	 * If we are on the alternate signal stack and would overflow it, don't.
>  	 * Return an always-bogus address instead so we will die with SIGSEGV.
>  	 */
> -	if (onsigstack && !likely(on_sig_stack(sp)))
> +	if (onsigstack && unlikely(sp <= current->sas_ss_sp ||
> +				   sp - current->sas_ss_sp > current->sas_ss_size))
>  		return (void __user *)-1L;

So clearly I'm missing something because trying to trigger the test case
in the bugzilla:

https://bugzilla.kernel.org/show_bug.cgi?id=153531

on current tip/master doesn't work. Runs with MY_MINSIGSTKSZ under 2048
fail with:

tst-minsigstksz-2: sigaltstack: Cannot allocate memory

and above 2048 don't overwrite bytes below the stack.

So something else is missing. How did you test this patch?

Thx.

-- 
Regards/Gruss,
    Boris.

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