linux-kernel - [tip:x86/mm] x86/kprobes: Set instruction page as executable

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Message-ID: <tip-7298e24f904224fa79eb8fd7e0fbd78950ccf2db@git.kernel.org>
Date:   Tue, 30 Apr 2019 04:22:06 -0700
From:   tip-bot for Nadav Amit <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, namit@...are.com, mingo@...nel.org,
        akpm@...ux-foundation.org, tglx@...utronix.de,
        rick.p.edgecombe@...el.com, hpa@...or.com,
        ard.biesheuvel@...aro.org, dave.hansen@...ux.intel.com,
        torvalds@...ux-foundation.org, kristen@...ux.intel.com,
        linux_dti@...oud.com, bp@...en8.de, deneen.t.dock@...el.com,
        riel@...riel.com, luto@...nel.org, will.deacon@....com,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: [tip:x86/mm] x86/kprobes: Set instruction page as executable

Commit-ID:  7298e24f904224fa79eb8fd7e0fbd78950ccf2db
Gitweb:     https://git.kernel.org/tip/7298e24f904224fa79eb8fd7e0fbd78950ccf2db
Author:     Nadav Amit <namit@...are.com>
AuthorDate: Thu, 25 Apr 2019 17:11:30 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 30 Apr 2019 12:37:54 +0200

x86/kprobes: Set instruction page as executable

Set the page as executable after allocation.  This patch is a
preparatory patch for a following patch that makes module allocated
pages non-executable.

While at it, do some small cleanup of what appears to be unnecessary
masking.

Signed-off-by: Nadav Amit <namit@...are.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: <akpm@...ux-foundation.org>
Cc: <ard.biesheuvel@...aro.org>
Cc: <deneen.t.dock@...el.com>
Cc: <kernel-hardening@...ts.openwall.com>
Cc: <kristen@...ux.intel.com>
Cc: <linux_dti@...oud.com>
Cc: <will.deacon@....com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Rik van Riel <riel@...riel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: https://lkml.kernel.org/r/20190426001143.4983-11-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/kprobes/core.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index fed46ddb1eef..06058c44ab57 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -431,8 +431,20 @@ void *alloc_insn_page(void)
 	void *page;
 
 	page = module_alloc(PAGE_SIZE);
-	if (page)
-		set_memory_ro((unsigned long)page & PAGE_MASK, 1);
+	if (!page)
+		return NULL;
+
+	/*
+	 * First make the page read-only, and only then make it executable to
+	 * prevent it from being W+X in between.
+	 */
+	set_memory_ro((unsigned long)page, 1);
+
+	/*
+	 * TODO: Once additional kernel code protection mechanisms are set, ensure
+	 * that the page was not maliciously altered and it is still zeroed.
+	 */
+	set_memory_x((unsigned long)page, 1);
 
 	return page;
 }
@@ -440,8 +452,12 @@ void *alloc_insn_page(void)
 /* Recover page to RW mode before releasing it */
 void free_insn_page(void *page)
 {
-	set_memory_nx((unsigned long)page & PAGE_MASK, 1);
-	set_memory_rw((unsigned long)page & PAGE_MASK, 1);
+	/*
+	 * First make the page non-executable, and only then make it writable to
+	 * prevent it from being W+X in between.
+	 */
+	set_memory_nx((unsigned long)page, 1);
+	set_memory_rw((unsigned long)page, 1);
 	module_memfree(page);
 }