Re: [PATCH v3 27/37] x86/shstk: Introduce routines modifying shstk

[Peter Zijlstra]

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() ?

Should you write a 64bit value even if the task receiving a signal is
32bit ?