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

Josh Poimboeuf
2025-02-07T21:06:16Z

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))