Messages in this thread | | | From | "Edgecombe, Rick P" <> | Subject | Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk | Date | Tue, 15 Nov 2022 23:42:46 +0000 |
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On Tue, 2022-11-15 at 15:18 +0100, Peter Zijlstra wrote: > On Fri, Nov 04, 2022 at 03:35:54PM -0700, Rick Edgecombe wrote: > > > +#ifdef CONFIG_X86_USER_SHADOW_STACK > > +static inline int write_user_shstk_64(u64 __user *addr, u64 val) > > +{ > > + asm_volatile_goto("1: wrussq %[val], (%[addr])\n" > > + _ASM_EXTABLE(1b, %l[fail]) > > + :: [addr] "r" (addr), [val] "r" (val) > > + :: fail); > > + return 0; > > +fail: > > + return -EFAULT; > > +} > > +#endif /* CONFIG_X86_USER_SHADOW_STACK */ > > Why isn't this modelled after put_user() ?
You mean as far as supporting multiple sizes? It just isn't really needed yet. We are only writing single frames. I suppose it might make more sense with the alt shadow stack support, but that is dropped for now.
The other difference here is that WRUSS is a weird instruction that is treated as a user access even if it comes from the kernel mode. So it's doesn't need to stac/clac.
> > Should you write a 64bit value even if the task receiving a signal is > 32bit ?
32 bit support was also dropped.
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