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SubjectRe: [PATCH v1 1/1] vsprintf: Fix potential unaligned access
Hi Andy,

On Mon, Jan 10, 2022 at 10:50:49PM +0200, Andy Shevchenko wrote:
> The %p4cc specifier in some cases might get an unaligned pointer.
> Due to this we need to make copy to local variable once to avoid
> potential crashes on some architectures due to improper access.

I guess this problem exists virtually everywhere where pointers are being
handled: the pointer could be unaligned. Does this even address the false
positive compiler warning?

>
> Fixes: af612e43de6d ("lib/vsprintf: Add support for printing V4L2 and DRM fourccs")
> Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> lib/vsprintf.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index c130dcaca5e2..b02f01366acb 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -49,6 +49,7 @@
>
> #include <asm/page.h> /* for PAGE_SIZE */
> #include <asm/byteorder.h> /* cpu_to_le16 */
> +#include <asm/unaligned.h>
>
> #include <linux/string_helpers.h>
> #include "kstrtox.h"
> @@ -1761,7 +1762,7 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
> char output[sizeof("0123 little-endian (0x01234567)")];
> char *p = output;
> unsigned int i;
> - u32 val;
> + u32 orig, val;
>
> if (fmt[1] != 'c' || fmt[2] != 'c')
> return error_string(buf, end, "(%p4?)", spec);
> @@ -1769,21 +1770,22 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
> if (check_pointer(&buf, end, fourcc, spec))
> return buf;
>
> - val = *fourcc & ~BIT(31);
> + orig = get_unaligned(fourcc);
> + val = orig & ~BIT(31);
>
> - for (i = 0; i < sizeof(*fourcc); i++) {
> + for (i = 0; i < sizeof(u32); i++) {
> unsigned char c = val >> (i * 8);
>
> /* Print non-control ASCII characters as-is, dot otherwise */
> *p++ = isascii(c) && isprint(c) ? c : '.';
> }
>
> - strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
> + strcpy(p, orig & BIT(31) ? " big-endian" : " little-endian");
> p += strlen(p);
>
> *p++ = ' ';
> *p++ = '(';
> - p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, sizeof(u32));
> + p = special_hex_number(p, output + sizeof(output) - 2, orig, sizeof(u32));
> *p++ = ')';
> *p = '\0';
>

--
Kind regards,

Sakari Ailus

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