lkml.org 
[lkml]   [2019]   [Dec]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: Build regressions/improvements in v5.5-rc2
Hi Greg,

On Mon, Dec 16, 2019 at 9:38 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Below is the list of build error/warning regressions/improvements in
> v5.5-rc2[1] compared to v5.4[2].

> [1] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/d1eef1c619749b2a57e514a3fa67d9a516ffa919/ (all 232 configs)
> [2] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/219d54332a09e8d8741c1e1982f5eae56099de85/ (all 232 configs)

> + /kisskb/src/arch/m68k/include/asm/string.h: warning: '__builtin_memcpy' forming offset [3, 4] is out of the bounds [0, 2] of object '__gu_val' with type 'short unsigned int' [-Warray-bounds]: => 72:25

The upgrade from gcc 4.6.3 to 81.0 seems to have revealed a potential
issue in get_user() in arch/m68k/include/asm/uaccess_no.h.

#define get_user(x, ptr) \
({ \
int __gu_err = 0; \
typeof(x) __gu_val = 0; \
^^^^^^^^^
This is the type of the destination

switch (sizeof(*(ptr))) { \
case 1: \
__get_user_asm(__gu_err, __gu_val, ptr, b, "=d"); \
break; \
case 2: \
__get_user_asm(__gu_err, __gu_val, ptr, w, "=r"); \
break; \
case 4: \
__get_user_asm(__gu_err, __gu_val, ptr, l, "=r"); \
break; \
case 8: \
memcpy((void *) &__gu_val, ptr, sizeof (*(ptr))); \
break; \
default: \
__gu_val = 0; \
__gu_err = __get_user_bad(); \
break; \
} \
(x) = (typeof(*(ptr))) __gu_val; \
__gu_err; \
})

ext2_ioctl() calls this like

unsigned short rsv_window_size;
if (get_user(rsv_window_size, (int __user *)arg)) { ... }

So a 32-bit value is being copied to an unsigned short value, leading
to the warning (for the memcpy() in the non-taken "case 8" branch).

Fortunately the compiler emits a register move for this, so no real harm
is done:

| fs/ext2/ioctl.c:123: if (get_user(rsv_window_size,
(int __user *)arg))
move.l 48(%sp),%a0 | arg,
#APP
| 123 "fs/ext2/ioctl.c" 1
movel (%a0),%d2 | *arg.32_43, __gu_val

The corresponding code in arch/m68k/include/asm/uaccess_mm.h
uses a temporary __gu_val of the right sized type based on the source
type to avoid this.


Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds

\
 
 \ /
  Last update: 2019-12-16 09:50    [W:0.037 / U:1.372 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site