From: Arnd Bergmann
> Sent: 17 May 2021 21:34
>
> The compat version of sys_kexec_load() uses compat_alloc_user_space to
> convert the user-provided arguments into the native format.
>
> Move the conversion into the regular implementation with
> an in_compat_syscall() check to simplify it and avoid the
> compat_alloc_user_space() call.
>
> compat_sys_kexec_load() now behaves the same as sys_kexec_load().
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> include/linux/kexec.h | 2 -
> kernel/kexec.c | 95 +++++++++++++++++++------------------------
> 2 files changed, 42 insertions(+), 55 deletions(-)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 0c994ae37729..f61e310d7a85 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -88,14 +88,12 @@ struct kexec_segment {
> size_t memsz;
> };
>
> -#ifdef CONFIG_COMPAT
> struct compat_kexec_segment {
> compat_uptr_t buf;
> compat_size_t bufsz;
> compat_ulong_t mem; /* User space sees this as a (void *) ... */
> compat_size_t memsz;
> };
> -#endif
>
> #ifdef CONFIG_KEXEC_FILE
> struct purgatory_info {
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index c82c6c06f051..6618b1d9f00b 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -19,21 +19,46 @@
>
> #include "kexec_internal.h"
>
> +static int copy_user_compat_segment_list(struct kimage *image,
> + unsigned long nr_segments,
> + void __user *segments)
> +{
> + struct compat_kexec_segment __user *cs = segments;
> + struct compat_kexec_segment segment;
> + int i;
> +
> + for (i = 0; i < nr_segments; i++) {
> + if (copy_from_user(&segment, &cs[i], sizeof(segment)))
> + return -EFAULT;
How many segments are there?
The multiple copy_from_user() will be slow.
> +
> + image->segment[i] = (struct kexec_segment) {
> + .buf = compat_ptr(segment.buf),
> + .bufsz = segment.bufsz,
> + .mem = segment.mem,
> + .memsz = segment.memsz,
> + };
> + }
> +
> + return 0;
> +}
> +
> +
> static int copy_user_segment_list(struct kimage *image,
> unsigned long nr_segments,
> struct kexec_segment __user *segments)
> {
> - int ret;
> size_t segment_bytes;
>
> /* Read in the segments */
> image->nr_segments = nr_segments;
> segment_bytes = nr_segments * sizeof(*segments);
Should there be a bound check on nr_segments?
I can't see one in the code in this patch.
> - ret = copy_from_user(image->segment, segments, segment_bytes);
> - if (ret)
> - ret = -EFAULT;
> + if (in_compat_syscall())
> + return copy_user_compat_segment_list(image, nr_segments, segments);
>
> - return ret;
> + if (copy_from_user(image->segment, segments, segment_bytes))
> + return -EFAULT;
> +
> + return 0;
An alternate sequence (which Eric will like even less!) is to
do a single copy_from_user() for the entire compat size array
into the 'normal' buffer and then do a reverse order conversion
of each array entry from 'compat' to '64 bit'.
David
-
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