FAILED: patch "[PATCH] s390/mm: do not trigger write fault when vma does not allow" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 41ac42f137080bc230b5882e3c88c392ab7f2d32 Mon Sep 17 00:00:00 2001
From: Gerald Schaefer <[email protected]>
Date: Wed, 17 Aug 2022 15:26:03 +0200
Subject: [PATCH] s390/mm: do not trigger write fault when vma does not allow
VM_WRITE

For non-protection pXd_none() page faults in do_dat_exception(), we call do_exception() with access == (VM_READ | VM_WRITE | VM_EXEC). In do_exception(), vma->vm_flags is checked against that before calling handle_mm_fault().

Since commit 92f842eac7ee3 ("[S390] store indication fault optimization"), we call handle_mm_fault() with FAULT_FLAG_WRITE, when recognizing that it was a write access. However, the vma flags check is still only checking against (VM_READ | VM_WRITE | VM_EXEC), and therefore also calling handle_mm_fault() with FAULT_FLAG_WRITE in cases where the vma does not allow VM_WRITE.

Fix this by changing access check in do_exception() to VM_WRITE only, when recognizing write access.

index 13449941516c..09b6e756d521 100644
@@ -379,7 +379,9 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	flags = FAULT_FLAG_DEFAULT;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
-	if (access == VM_WRITE || is_write)
+	if (is_write)
+		access = VM_WRITE;
+	if (access == VM_WRITE)
 		flags |= FAULT_FLAG_WRITE;
 	mmap_read_lock(mm);
 

commit 41ac42f137080bc230b5882e3c88c392ab7f2d32 upstream.

For non-protection pXd_none() page faults in do_dat_exception(), we call do_exception() with access == (VM_READ | VM_WRITE | VM_EXEC). In do_exception(), vma->vm_flags is checked against that before calling handle_mm_fault().

Since commit 92f842eac7ee3 ("[S390] store indication fault optimization"), we call handle_mm_fault() with FAULT_FLAG_WRITE, when recognizing that it was a write access. However, the vma flags check is still only checking against (VM_READ | VM_WRITE | VM_EXEC), and therefore also calling handle_mm_fault() with FAULT_FLAG_WRITE in cases where the vma does not allow VM_WRITE.

Fix this by changing access check in do_exception() to VM_WRITE only, when recognizing write access.

---
 arch/s390/mm/fault.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

index a6e3c7022245..d64b180caeda 100644
@@ -455,7 +455,9 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
 	flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
 	if (user_mode(regs))
 		flags |= FAULT_FLAG_USER;
-	if (access == VM_WRITE || (trans_exc_code & store_indication) == 0x400)
+	if ((trans_exc_code & store_indication) == 0x400)
+		access = VM_WRITE;
+	if (access == VM_WRITE)
 		flags |= FAULT_FLAG_WRITE;
 	down_read(&mm->mmap_sem);
 

2.34.1