linux-hardening - [PATCH 2/6] PKEY: Add arch_check_pkey_enforce

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Message-ID: <20230515130553.2311248-3-jeffxu@chromium.org>
Date:   Mon, 15 May 2023 13:05:48 +0000
From:   jeffxu@...omium.org
To:     dave.hansen@...el.com, luto@...nel.org, jorgelo@...omium.org,
        keescook@...omium.org, groeck@...omium.org, jannh@...gle.com,
        sroettger@...gle.com
Cc:     akpm@...ux-foundation.org, jeffxu@...gle.com,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org
Subject: [PATCH 2/6] PKEY: Add arch_check_pkey_enforce_api()

From: Jeff Xu <jeffxu@...gle.com>

This patch adds an architecture-independent function,
arch_check_pkey_enforce_api(), that checks whether the calling thread
has write access to the PKRU for a given range of memory. If the
memory range is protected by PKEY_ENFORCE_API, then the thread must
have write access to the PKRU in order to make changes to the memory
mapping (such as mprotect/munmap).

This function is used by the kernel to enforce the
PKEY_ENFORCE_API flag.

Signed-off-by: Jeff Xu<jeffxu@...gle.com>
---
 arch/powerpc/include/asm/pkeys.h |  8 +++++
 arch/x86/include/asm/pkeys.h     | 50 ++++++++++++++++++++++++++++++++
 include/linux/pkeys.h            |  9 ++++++
 3 files changed, 67 insertions(+)

diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
index 943333ac0fee..24c481e5e95b 100644
--- a/arch/powerpc/include/asm/pkeys.h
+++ b/arch/powerpc/include/asm/pkeys.h
@@ -177,5 +177,13 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)
 	return true;
 }
 
+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+					      unsigned long start,
+					      unsigned long end)
+{
+	/* Allow by default */
+	return 0;
+}
+
 extern void pkey_mm_init(struct mm_struct *mm);
 #endif /*_ASM_POWERPC_KEYS_H */
diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h
index ecadf04a8251..8b94ffc4ca32 100644
--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -161,4 +161,54 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)
 
 	return true;
 }
+
+static inline int __arch_check_vma_pkey_for_write(struct vm_area_struct *vma)
+{
+	int pkey = vma_pkey(vma);
+
+	if (mm_pkey_enforce_api(vma->vm_mm, pkey)) {
+		if (!__pkru_allows_write(read_pkru(), pkey))
+			return -EACCES;
+	}
+
+	return 0;
+}
+
+/*
+ * arch_check_pkey_enforce_api is used by the kernel to enforce
+ * PKEY_ENFORCE_API flag.
+ * It checks whether the calling thread  has write access to the PKRU
+ * for a given range of memory. If the  memory range is protected by
+ * PKEY_ENFORCE_API, then the thread must  have write access to the
+ * PKRU in order to make changes to the memory  mapping, such as
+ * mprotect/munmap.
+ */
+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+					      unsigned long start,
+					      unsigned long end)
+{
+	int error;
+	struct vm_area_struct *vma;
+
+	if (!arch_pkeys_enabled())
+		return 0;
+
+	while (true) {
+		vma = find_vma_intersection(mm, start, end);
+		if (!vma)
+			break;
+
+		error = __arch_check_vma_pkey_for_write(vma);
+		if (error)
+			return error;
+
+		if (vma->vm_end >= end)
+			break;
+
+		start = vma->vm_end;
+	}
+
+	return 0;
+}
+
 #endif /*_ASM_X86_PKEYS_H */
diff --git a/include/linux/pkeys.h b/include/linux/pkeys.h
index 81a482c3e051..7b00689e1c24 100644
--- a/include/linux/pkeys.h
+++ b/include/linux/pkeys.h
@@ -53,6 +53,15 @@ static inline bool arch_check_pkey_alloc_flags(unsigned long flags)
 		return false;
 	return true;
 }
+
+static inline int arch_check_pkey_enforce_api(struct mm_struct *mm,
+					      unsigned long start,
+					      unsigned long end)
+{
+	// Allow by default.
+	return 0;
+}
+
 #endif /* ! CONFIG_ARCH_HAS_PKEYS */
 
 #endif /* _LINUX_PKEYS_H */
-- 
2.40.1.606.ga4b1b128d6-goog