On Thu, Jul 25, 2019 at 12:48 AM Josh Poimboeuf <jpoim...@redhat.com> wrote:
>
> Objtool reports:
>
> drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool:
> .altinstr_replacement+0x36: redundant UACCESS disable
>
> __copy_from_user() already does both STAC and CLAC, so the
> user_access_end() in its error path adds an extra unnecessary CLAC.
>
> Fixes: 0b2c8f8b6b0c ("i915: fix missing user_access_end() in page fault
> exception case")
> Reported-by: Thomas Gleixner <t...@linutronix.de>
> Reported-by: Sedat Dilek <sedat.di...@gmail.com>
> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> Tested-by: Nick Desaulniers <ndesaulni...@google.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/617
> Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
Just for the records and ensuing ages:
Tested-by: Sedat Dilek <sedat.di...@gmail.com>
> ---
> .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 20 +++++++++----------
> 1 file changed, 9 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> index 5fae0e50aad0..41dab9ea33cd 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> @@ -1628,6 +1628,7 @@ static int check_relocations(const struct
> drm_i915_gem_exec_object2 *entry)
>
> static int eb_copy_relocations(const struct i915_execbuffer *eb)
> {
> + struct drm_i915_gem_relocation_entry *relocs;
> const unsigned int count = eb->buffer_count;
> unsigned int i;
> int err;
> @@ -1635,7 +1636,6 @@ static int eb_copy_relocations(const struct
> i915_execbuffer *eb)
> for (i = 0; i < count; i++) {
> const unsigned int nreloc = eb->exec[i].relocation_count;
> struct drm_i915_gem_relocation_entry __user *urelocs;
> - struct drm_i915_gem_relocation_entry *relocs;
> unsigned long size;
> unsigned long copied;
>
> @@ -1663,14 +1663,8 @@ static int eb_copy_relocations(const struct
> i915_execbuffer *eb)
>
> if (__copy_from_user((char *)relocs + copied,
> (char __user *)urelocs + copied,
> - len)) {
> -end_user:
> - user_access_end();
> -end:
> - kvfree(relocs);
> - err = -EFAULT;
> - goto err;
> - }
> + len))
> + goto end;
>
> copied += len;
> } while (copied < size);
> @@ -1699,10 +1693,14 @@ static int eb_copy_relocations(const struct
> i915_execbuffer *eb)
>
> return 0;
>
> +end_user:
> + user_access_end();
> +end:
> + kvfree(relocs);
> + err = -EFAULT;
> err:
> while (i--) {
> - struct drm_i915_gem_relocation_entry *relocs =
> - u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
> + relocs = u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
> if (eb->exec[i].relocation_count)
> kvfree(relocs);
> }
> --
> 2.20.1
>
