Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading .sframe contents

[Josh Poimboeuf]

On Wed, Feb 05, 2025 at 10:47:58AM +0100, Jens Remus wrote:
> UNSAFE_GET_USER_INC(ra_off, cur, offset_size, Efault);
> 
> With offset_size=1 expands into:
> 
> __UNSAFE_GET_USER_INC(/*to=*/ra_off, /*from=*cur, /*type=*/u8, /*label=*/Efault);
> 
> Expands into:
> 
> {
> 	u8 __to;
> 	unsafe_get_user(__to, (u8 __user *)cur, Efault);
> 	cur += sizeof(__to);
> 	ra_off = (typeof(ra_off))__to;
> }
> 
> The issue is that on the last line __to is u8 instead of s8 and thus
> u8 gets casted to s32, which is performed without sign extension.  __to
> would need to be s8 or get casted to s8 for sign extension to take
> place.

Ah, I get it now, thanks for spelling that out for me.

Here's what I have at the moment:

#define __UNSAFE_GET_USER_INC(to, from, type, label)			\
({									\
	type __to;							\
	unsafe_get_user(__to, (type __user *)from, label);		\
	from += sizeof(__to);						\
	to = __to;							\
})

#define __UNSAFE_GET_USER_INC(to, from, size, label, u_or_s)		\
({									\
	switch (size) {							\
	case 1:								\
		__UNSAFE_GET_USER_INC(to, from, u_or_s##8, label);	\
		break;							\
	case 2:								\
		__UNSAFE_GET_USER_INC(to, from, u_or_s##16, label);	\
		break;							\
	case 4:								\
		__UNSAFE_GET_USER_INC(to, from, u_or_s##32, label);	\
		break;							\
	default:							\
		dbg_sec_uaccess("%d: bad unsafe_get_user() size %u\n",	\
				__LINE__, size);			\
		return -EFAULT;						\
	}								\
})

#define UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label)		\
	__UNSAFE_GET_USER_INC(to, from, size, label, u)

#define UNSAFE_GET_USER_SIGNED_INC(to, from, size, label)		\
	__UNSAFE_GET_USER_INC(to, from, size, label, s)

#define UNSAFE_GET_USER_INC(to, from, size, label)				\
	_Generic(to,								\
		 u8:	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
		 u16:	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
		 u32:	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
		 s8:	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
		 s16:	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
		 s32:	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label))