Skip to content

Commit

Permalink
drm/vmwgfx: Add unwind hints around RBP clobber
Browse files Browse the repository at this point in the history
VMware high-bandwidth hypercalls take the RBP register as input.  This
breaks basic frame pointer convention, as RBP should never be clobbered.

So frame pointer unwinding is broken for the instructions surrounding
the hypercalls.  Fortunately this doesn't break live patching with
CONFIG_FRAME_POINTER, as it only unwinds from blocking tasks, and stack
traces from preempted tasks are already marked unreliable anyway.

However, for live patching with ORC, this could actually be a
theoretical problem if vmw_port_hb_{in,out}() were still compiled with a
frame pointer due to having an aligned stack.  In practice that hasn't
seemed to be an issue since the objtool warnings have only been seen
with CONFIG_FRAME_POINTER.

Add unwind hint annotations to tell the ORC unwinder to mark stack
traces as unreliable.

Fixes the following warnings:

  vmlinux.o: warning: objtool: vmw_port_hb_in+0x1df: return with modified stack frame
  vmlinux.o: warning: objtool: vmw_port_hb_out+0x1dd: return with modified stack frame

Fixes: 89da76f ("drm/vmwgfx: Add VMWare host messaging capability")
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202305160135.97q0Elax-lkp@intel.com/
Link: https://lore.kernel.org/r/4c795f2d87bc0391cf6543bcb224fa540b55ce4b.1685981486.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
  • Loading branch information
Josh Poimboeuf committed Jun 7, 2023
1 parent 1e4b619 commit a9da824
Show file tree
Hide file tree
Showing 2 changed files with 21 additions and 4 deletions.
9 changes: 9 additions & 0 deletions arch/x86/include/asm/unwind_hints.h
Original file line number Diff line number Diff line change
Expand Up @@ -76,9 +76,18 @@

#else

#define UNWIND_HINT_UNDEFINED \
UNWIND_HINT(UNWIND_HINT_TYPE_UNDEFINED, 0, 0, 0)

#define UNWIND_HINT_FUNC \
UNWIND_HINT(UNWIND_HINT_TYPE_FUNC, ORC_REG_SP, 8, 0)

#define UNWIND_HINT_SAVE \
UNWIND_HINT(UNWIND_HINT_TYPE_SAVE, 0, 0, 0)

#define UNWIND_HINT_RESTORE \
UNWIND_HINT(UNWIND_HINT_TYPE_RESTORE, 0, 0, 0)

#endif /* __ASSEMBLY__ */

#endif /* _ASM_X86_UNWIND_HINTS_H */
16 changes: 12 additions & 4 deletions drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
Original file line number Diff line number Diff line change
Expand Up @@ -105,10 +105,14 @@
flags, magic, bp, \
eax, ebx, ecx, edx, si, di) \
({ \
asm volatile ("push %%rbp;" \
asm volatile ( \
UNWIND_HINT_SAVE \
"push %%rbp;" \
UNWIND_HINT_UNDEFINED \
"mov %12, %%rbp;" \
VMWARE_HYPERCALL_HB_OUT \
"pop %%rbp;" : \
"pop %%rbp;" \
UNWIND_HINT_RESTORE : \
"=a"(eax), \
"=b"(ebx), \
"=c"(ecx), \
Expand All @@ -130,10 +134,14 @@
flags, magic, bp, \
eax, ebx, ecx, edx, si, di) \
({ \
asm volatile ("push %%rbp;" \
asm volatile ( \
UNWIND_HINT_SAVE \
"push %%rbp;" \
UNWIND_HINT_UNDEFINED \
"mov %12, %%rbp;" \
VMWARE_HYPERCALL_HB_IN \
"pop %%rbp" : \
"pop %%rbp;" \
UNWIND_HINT_RESTORE : \
"=a"(eax), \
"=b"(ebx), \
"=c"(ecx), \
Expand Down

0 comments on commit a9da824

Please sign in to comment.