Messages in this thread | | | Date | Thu, 26 Jul 2018 11:44:58 +0100 | From | Dave Martin <> | Subject | Re: [PATCH 1/2] signal: Introduce COMPAT_SIGMINSTKSZ for use in compat_sys_sigaltstack |
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On Wed, Jul 25, 2018 at 05:37:26PM +0100, Will Deacon wrote: > On Wed, Jul 25, 2018 at 04:54:27PM +0100, Dave Martin wrote: > > On Wed, Jul 25, 2018 at 02:45:11PM +0100, Will Deacon wrote: > > > @@ -3476,7 +3478,8 @@ int restore_altstack(const stack_t __user *uss) > > > stack_t new; > > > if (copy_from_user(&new, uss, sizeof(stack_t))) > > > return -EFAULT; > > > - (void)do_sigaltstack(&new, NULL, current_user_stack_pointer()); > > > + (void)do_sigaltstack(&new, NULL, current_user_stack_pointer(), > > > + MINSIGSTKSZ); > > > > Why can't this fail? > > > > If this fails here we silently go wrong, but... > > > > > /* squash all but EFAULT for now */ > > > return 0; > > > } > > > @@ -3510,7 +3513,8 @@ static int do_compat_sigaltstack(const compat_stack_t __user *uss_ptr, > > > uss.ss_size = uss32.ss_size; > > > } > > > ret = do_sigaltstack(uss_ptr ? &uss : NULL, &uoss, > > > - compat_user_stack_pointer()); > > > + compat_user_stack_pointer(), > > > + COMPAT_MINSIGSTKSZ); > > > > If this fails on arm64, we seem to SEGV (see compat_sys_rt_sigreturn()). > > > > This patch doesn't introduce this inconsistency, this might be a good > > opportunity to clean it up. > > I don't think there's an inconsistency here -- both restore_altstack and > compat_restore_altstack suppress all non--EFAULT errors (remember that uoss > is NULL in both cases, so the copy_from_user() immediately before the > do_sigaltstack() call for the native path is all we care about). I think the > behaviour is: on a sigreturn, if you set the altstack to be an unmapped > address then you get a SEGV, otherwise if you make it invalid in some other > way (e.g. too small) then it's ignored and the old altstack remains intact.
OK, I think I've satisfied myself that they do the same thing for now.
The code for the paths is a bit different, so it's not trivial to see that they have the same effect...
Cheers ---Dave
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