Quoting Josh Poimboeuf (2020-02-27 22:08:26) > With CONFIG_CC_OPTIMIZE_FOR_SIZE, objtool reports: > > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: i915_gem_execbuffer2_ioctl()+0x5b7: call to gen8_canonical_addr() with UACCESS enabled > > This means i915_gem_execbuffer2_ioctl() is calling gen8_canonical_addr() > -- and indirectly, sign_extend64() -- from the user_access_begin/end > critical region (i.e, with SMAP disabled). > > While it's probably harmless in this case, in general we like to avoid > extra function calls in SMAP-disabled regions because it can open up > inadvertent security holes. > > Fix it by moving the gen8_canonical_addr() conversion to a separate loop > before user_access_begin() is called. > > Note that gen8_canonical_addr() is now called *before* masking off the > PIN_OFFSET_MASK bits. That should be ok because it just does a sign > extension and ignores the masked lower bits anyway. > > Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > --- > drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > index d5a0f5ae4a8b..183cab13e028 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c > @@ -2947,6 +2947,13 @@ i915_gem_execbuffer2_ioctl(struct drm_device *dev, void *data, > u64_to_user_ptr(args->buffers_ptr); > unsigned int i; > > + /* > + * Do the call to gen8_canonical_addr() outside the > + * uaccess-enabled region to minimize uaccess exposure. > + */ > + for (i = 0; i < args->buffer_count; i++) > + exec2_list[i].offset = gen8_canonical_addr(exec2_list[i].offset); Another loop over all the objects, where we intentionally try and skip unmodified entries? To save 2 instructions from inside the second loop? Colour me skeptical. -Chris _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
