linux-kernel - [PATCH] sparc64: Use arch_validate

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Date:   Fri, 23 Oct 2020 11:56:11 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     jannh@...gle.com, hch@...radead.org, catalin.marinas@....com,
        davem@...emloft.net, akpm@...ux-foundation.org
Cc:     Khalid Aziz <khalid.aziz@...cle.com>, anthony.yznaga@...cle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org
Subject: [PATCH] sparc64: Use arch_validate_flags() to validate ADI flag

When userspace calls mprotect() to enable ADI on an address range,
do_mprotect_pkey() calls arch_validate_prot() to validate new
protection flags. arch_validate_prot() for sparc looks at the first
VMA associated with address range to verify if ADI can indeed be
enabled on this address range. This has two issues - (1) Address
range might cover multiple VMAs while arch_validate_prot() looks at
only the first VMA, (2) arch_validate_prot() peeks at VMA without
holding mmap lock which can result in race condition.

arch_validate_flags() from commit c462ac288f2c ("mm: Introduce
arch_validate_flags()") allows for VMA flags to be validated for all
VMAs that cover the address range given by user while holding mmap
lock. This patch updates sparc code to move the VMA check from
arch_validate_prot() to arch_validate_flags() to fix above two
issues.

Suggested-by: Jann Horn <jannh@...gle.com>
Suggested-by: Christoph Hellwig <hch@...radead.org>
Suggested-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
---
 arch/sparc/include/asm/mman.h | 54 +++++++++++++++++++----------------
 1 file changed, 29 insertions(+), 25 deletions(-)

diff --git a/arch/sparc/include/asm/mman.h b/arch/sparc/include/asm/mman.h
index f94532f25db1..274217e7ed70 100644
--- a/arch/sparc/include/asm/mman.h
+++ b/arch/sparc/include/asm/mman.h
@@ -57,35 +57,39 @@ static inline int sparc_validate_prot(unsigned long prot, unsigned long addr)
 {
 	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_ADI))
 		return 0;
-	if (prot & PROT_ADI) {
-		if (!adi_capable())
-			return 0;
+	return 1;
+}
 
-		if (addr) {
-			struct vm_area_struct *vma;
+#define arch_validate_flags(vm_flags) arch_validate_flags(vm_flags)
+/* arch_validate_flags() - Ensure combination of flags is valid for a
+ *	VMA.
+ */
+static inline bool arch_validate_flags(unsigned long vm_flags)
+{
+	/* If ADI is being enabled on this VMA, check for ADI
+	 * capability on the platform and ensure VMA is suitable
+	 * for ADI
+	 */
+	if (vm_flags & VM_SPARC_ADI) {
+		if (!adi_capable())
+			return false;
 
-			vma = find_vma(current->mm, addr);
-			if (vma) {
-				/* ADI can not be enabled on PFN
-				 * mapped pages
-				 */
-				if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
-					return 0;
+		/* ADI can not be enabled on PFN mapped pages */
+		if (vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+			return false;
 
-				/* Mergeable pages can become unmergeable
-				 * if ADI is enabled on them even if they
-				 * have identical data on them. This can be
-				 * because ADI enabled pages with identical
-				 * data may still not have identical ADI
-				 * tags on them. Disallow ADI on mergeable
-				 * pages.
-				 */
-				if (vma->vm_flags & VM_MERGEABLE)
-					return 0;
-			}
-		}
+		/* Mergeable pages can become unmergeable
+		 * if ADI is enabled on them even if they
+		 * have identical data on them. This can be
+		 * because ADI enabled pages with identical
+		 * data may still not have identical ADI
+		 * tags on them. Disallow ADI on mergeable
+		 * pages.
+		 */
+		if (vm_flags & VM_MERGEABLE)
+			return false;
 	}
-	return 1;
+	return true;
 }
 #endif /* CONFIG_SPARC64 */
 
-- 
2.25.1