linux-hardening - [PATCH 3/6] PKEY: Apply PKEY_ENFORCE

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Message-ID: <20230515130553.2311248-4-jeffxu@chromium.org>
Date:   Mon, 15 May 2023 13:05:49 +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 3/6] PKEY: Apply PKEY_ENFORCE_API to mprotect

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

This patch enables PKEY_ENFORCE_API for the mprotect and
mprotect_pkey syscalls.

Signed-off-by: Jeff Xu<jeffxu@...gle.com>
---
 mm/mprotect.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 8a68fdca8487..1378be50567d 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -727,9 +727,13 @@ mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
 
 /*
  * pkey==-1 when doing a legacy mprotect()
+ * syscall==true if this is called by syscall from userspace.
+ * Note: this is always true for now, added as a reminder in case that
+ * do_mprotect_pkey is called directly by kernel in the future.
+ * Also it is consistent with __do_munmap().
  */
 static int do_mprotect_pkey(unsigned long start, size_t len,
-		unsigned long prot, int pkey)
+		unsigned long prot, int pkey, bool syscall)
 {
 	unsigned long nstart, end, tmp, reqprot;
 	struct vm_area_struct *vma, *prev;
@@ -794,6 +798,21 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		}
 	}
 
+	/*
+	 * When called by syscall from userspace, check if the calling
+	 * thread has the PKEY permission to modify the memory mapping.
+	 */
+	if (syscall &&
+	    arch_check_pkey_enforce_api(current->mm, start, end) < 0) {
+		char comm[TASK_COMM_LEN];
+
+		pr_warn_ratelimited(
+			"munmap was denied on PKEY_ENFORCE_API memory, pid=%d '%s'\n",
+			task_pid_nr(current), get_task_comm(comm, current));
+		error = -EACCES;
+		goto out;
+	}
+
 	prev = vma_prev(&vmi);
 	if (start > vma->vm_start)
 		prev = vma;
@@ -878,7 +897,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 		unsigned long, prot)
 {
-	return do_mprotect_pkey(start, len, prot, -1);
+	return do_mprotect_pkey(start, len, prot, -1, true);
 }
 
 #ifdef CONFIG_ARCH_HAS_PKEYS
@@ -886,7 +905,7 @@ SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 		unsigned long, prot, int, pkey)
 {
-	return do_mprotect_pkey(start, len, prot, pkey);
+	return do_mprotect_pkey(start, len, prot, pkey, true);
 }
 
 SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
-- 
2.40.1.606.ga4b1b128d6-goog