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From:   Yu-cheng Yu <yu-cheng.yu@intel.com>
To:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
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        Arnd Bergmann <arnd@arndb.de>,
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        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
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        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>,
        Haitao Huang <haitao.huang@intel.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH v24 20/30] mm/mprotect: Exclude shadow stack from preserve_write
Date:   Thu,  1 Apr 2021 15:10:54 -0700
Message-Id: <20210401221104.31584-21-yu-cheng.yu@intel.com>
In-Reply-To: <20210401221104.31584-1-yu-cheng.yu@intel.com>
References: <20210401221104.31584-1-yu-cheng.yu@intel.com>
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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
(RW=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>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
v24:
- Change arch_shadow_stack_mapping() to is_shadow_stack_mapping().

 mm/huge_memory.c | 7 ++++++-
 mm/mprotect.c    | 9 ++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 65fc0aedd577..1d41138c4f74 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1812,12 +1812,17 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 	bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
 	bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
 	bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
+	bool shstk = is_shadow_stack_mapping(vma->vm_flags);
 
 	ptl = __pmd_trans_huge_lock(pmd, vma);
 	if (!ptl)
 		return 0;
 
-	preserve_write = prot_numa && pmd_write(*pmd);
+	/*
+	 * Preserve only normal writable huge PMD, but not shadow
+	 * stack (RW=0, Dirty=1).
+	 */
+	preserve_write = prot_numa && pmd_write(*pmd) && !shstk;
 	ret = 1;
 
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
diff --git a/mm/mprotect.c b/mm/mprotect.c
index c1ce78d688b6..550448dc5ff1 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -75,7 +75,14 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 		oldpte = *pte;
 		if (pte_present(oldpte)) {
 			pte_t ptent;
-			bool preserve_write = prot_numa && pte_write(oldpte);
+			bool shstk = is_shadow_stack_mapping(vma->vm_flags);
+			bool preserve_write;
+
+			/*
+			 * Preserve only normal writable PTE, but not shadow
+			 * stack (RW=0, Dirty=1).
+			 */
+			preserve_write = prot_numa && pte_write(oldpte) && !shstk;
 
 			/*
 			 * Avoid trapping faults against the zero or KSM
-- 
2.21.0