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Cc:     rick.p.edgecombe@intel.com, Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: [PATCH v2 20/39] mm/mprotect: Exclude shadow stack from preserve_write
Date:   Thu, 29 Sep 2022 15:29:17 -0700
Message-Id: <20220929222936.14584-21-rick.p.edgecombe@intel.com>
In-Reply-To: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
Precedence: bulk

From: Yu-cheng Yu <yu-cheng.yu@intel.com>

In change_pte_range(), when a PTE is changed for prot_numa, _PAGE_RW is
preserved to avoid the additional write fault after the NUMA hinting fault.
However, pte_write() now includes both normal writable and shadow stack
(Write=0, Dirty=1) PTEs, but the latter does not have _PAGE_RW and has no
need to preserve it.

Exclude shadow stack from preserve_write test, and apply the same change to
change_huge_pmd().

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>

---

Yu-cheng v25:
 - Move is_shadow_stack_mapping() to a separate line.

Yu-cheng v24:
 - Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().

 mm/huge_memory.c | 7 +++++++
 mm/mprotect.c    | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 11fc69eb4717..492c4f190f55 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1800,6 +1800,13 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		return 0;
 
 	preserve_write = prot_numa && pmd_write(*pmd);
+
+	/*
+	 * Preserve only normal writable huge PMD, but not shadow
+	 * stack (RW=0, Dirty=1).
+	 */
+	if (vma->vm_flags & VM_SHADOW_STACK)
+		preserve_write = false;
 	ret = 1;
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
diff --git a/mm/mprotect.c b/mm/mprotect.c
index bc6bddd156ca..983206529dce 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -114,6 +114,13 @@ static unsigned long change_pte_range(struct mmu_gather *tlb,
 			pte_t ptent;
 			bool preserve_write = prot_numa && pte_write(oldpte);
 
+			/*
+			 * Preserve only normal writable PTE, but not shadow
+			 * stack (RW=0, Dirty=1).
+			 */
+			if (vma->vm_flags & VM_SHADOW_STACK)
+				preserve_write = false;
+
 			/*
 			 * Avoid trapping faults against the zero or KSM
 			 * pages. See similar comment in change_huge_pmd.
-- 
2.17.1