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SubjectRe: [PATCH] x86: uaccess: fix regression in unsafe_get_user
On Mon, Feb 18, 2019 at 11:15:44AM -0800, Andy Lutomirski wrote:
> diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
> index 58eacd41526c..709d6efe0d42 100644
> --- a/lib/strncpy_from_user.c
> +++ b/lib/strncpy_from_user.c
> @@ -10,12 +10,7 @@
> #include <asm/byteorder.h>
> #include <asm/word-at-a-time.h>
>
> -#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> -#define IS_UNALIGNED(src, dst) 0
> -#else
> -#define IS_UNALIGNED(src, dst) \
> - (((long) dst | (long) src) & (sizeof(long) - 1))
> -#endif
> +#define IS_UNALIGNED(addr) (((long)(addr)) & (sizeof(long) - 1))
>
> /*
> * Do a strncpy, return length of string without final '\0'.
> @@ -35,14 +30,39 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src, long
> if (max > count)
> max = count;
>
> - if (IS_UNALIGNED(src, dst))
> + /*
> + * First handle any unaligned prefix of src.
> + */
> + while (max && IS_UNALIGNED(src+res)) {

put spaces around the '+', below too.

> + char c;
> +
> + unsafe_get_user(c, src+res, efault);
> + dst[res] = c;
> + if (!c)
> + return res;
> + res++;
> + max--;
> + }
> +
> + /*
> + * Now we know that src + res is aligned. If dst is unaligned and
> + * we don't have efficient unaligned access, then keep going one
> + * byte at a time. (This could be optimized, but it would make
> + * the code more complicated.
> + */
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> + if (IS_UNALIGNED(dst + res))
> goto byte_at_a_time;
> +#endif
>
> while (max >= sizeof(unsigned long)) {
> + /*
> + * src + res is aligned, so the reads in this loop will
> + * not cross a page boundary.
> + */
> unsigned long c, data;
>
> - /* Fall back to byte-at-a-time if we get a page fault */
> - unsafe_get_user(c, (unsigned long __user *)(src+res), byte_at_a_time);
> + unsafe_get_user(c, (unsigned long __user *)(src+res), efault);
>
> *(unsigned long *)(dst+res) = c;
> if (has_zero(c, &data, &constants)) {
> @@ -54,7 +74,9 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src, long
> max -= sizeof(unsigned long);
> }
>
> -byte_at_a_time:

You can't remove that label - the ifndef above.

> + /*
> + * Finish the job one byte at a time.
> + */
> while (max) {
> char c;

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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