[PATCH 6.6.y] x86: shadow stacks: proper error handling for mmap lock

[Rick Edgecombe <rick.p.edgecombe@intel.com>]

From: Linus Torvalds <torvalds@linux-foundation.org>

[ Upstream commit 52f657e34d7b21b47434d9d8b26fa7f6778b63a0 ]

김영민 reports that shstk_pop_sigframe() doesn't check for errors from
mmap_read_lock_killable(), which is a silly oversight, and also shows
that we haven't marked those functions with "__must_check", which would
have immediately caught it.

So let's fix both issues.

Reported-by: 김영민 <osori@hspace.io>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Acked-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
 arch/x86/kernel/shstk.c   | 3 ++-
 include/linux/mmap_lock.h | 6 +++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index 19e4db582fb69..d259d7d5b962f 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -311,7 +311,8 @@ static int shstk_pop_sigframe(unsigned long *ssp)
 	need_to_check_vma = PAGE_ALIGN(*ssp) == *ssp;
 
 	if (need_to_check_vma)
-		mmap_read_lock_killable(current->mm);
+		if (mmap_read_lock_killable(current->mm))
+			return -EINTR;
 
 	err = get_shstk_data(&token_addr, (unsigned long __user *)*ssp);
 	if (unlikely(err))
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 8d38dcb6d044c..153e018677909 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -116,7 +116,7 @@ static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass)
 	__mmap_lock_trace_acquire_returned(mm, true, true);
 }
 
-static inline int mmap_write_lock_killable(struct mm_struct *mm)
+static inline int __must_check mmap_write_lock_killable(struct mm_struct *mm)
 {
 	int ret;
 
@@ -147,7 +147,7 @@ static inline void mmap_read_lock(struct mm_struct *mm)
 	__mmap_lock_trace_acquire_returned(mm, false, true);
 }
 
-static inline int mmap_read_lock_killable(struct mm_struct *mm)
+static inline int __must_check mmap_read_lock_killable(struct mm_struct *mm)
 {
 	int ret;
 
@@ -157,7 +157,7 @@ static inline int mmap_read_lock_killable(struct mm_struct *mm)
 	return ret;
 }
 
-static inline bool mmap_read_trylock(struct mm_struct *mm)
+static inline bool __must_check mmap_read_trylock(struct mm_struct *mm)
 {
 	bool ret;
 
-- 
2.54.0