[tip: objtool/core] drm/vmwgfx: Add unwind hints around RBP clobber

[tip-bot2 for Josh Poimboeuf]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     a9da8247627eefc73f909bf945031a5431a53993
Gitweb:        https://git.kernel.org/tip/a9da8247627eefc73f909bf945031a5431a53993
Author:        Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate:    Mon, 05 Jun 2023 09:12:22 -07:00
Committer:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
CommitterDate: Wed, 07 Jun 2023 10:03:12 -07:00

drm/vmwgfx: Add unwind hints around RBP clobber

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: 89da76fde68d ("drm/vmwgfx: Add VMWare host messaging capability")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Link: https://lore.kernel.org/oe-kbuild-all/202305160135.97q0Elax-lkp@xxxxxxxxx/
Link: https://lore.kernel.org/r/4c795f2d87bc0391cf6543bcb224fa540b55ce4b.1685981486.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/include/asm/unwind_hints.h     |  9 +++++++++
 drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h | 16 ++++++++++++----
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
index 01cb969..85cc57c 100644
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -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 */
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h b/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
index 0b74ca2..23899d7 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_msg_x86.h
@@ -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),				\
@@ -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),				\