LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Dave Hansen <dave.hansen@linux.intel.com>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, Dave Hansen <dave.hansen@linux.intel.com>,
	shakeelb@google.com, linuxram@us.ibm.com, tglx@linutronix.de,
	dave.hansen@intel.com, mpe@ellerman.id.au, mingo@kernel.org,
	akpm@linux-foundation.org, shuah@kernel.org
Subject: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC
Date: Fri, 23 Mar 2018 11:09:11 -0700	[thread overview]
Message-ID: <20180323180911.E43ACAB8@viggo.jf.intel.com> (raw)
In-Reply-To: <20180323180903.33B17168@viggo.jf.intel.com>


From: Dave Hansen <dave.hansen@linux.intel.com>

I got a bug report that the following code (roughly) was
causing a SIGSEGV:

	mprotect(ptr, size, PROT_EXEC);
	mprotect(ptr, size, PROT_NONE);
	mprotect(ptr, size, PROT_READ);
	*ptr = 100;

The problem is hit when the mprotect(PROT_EXEC)
is implicitly assigned a protection key to the VMA, and made
that key ACCESS_DENY|WRITE_DENY.  The PROT_NONE mprotect()
failed to remove the protection key, and the PROT_NONE->
PROT_READ left the PTE usable, but the pkey still in place
and left the memory inaccessible.

To fix this, we ensure that we always "override" the pkee
at mprotect() if the VMA does not have execute-only
permissions, but the VMA has the execute-only pkey.

We had a check for PROT_READ/WRITE, but it did not work
for PROT_NONE.  This entirely removes the PROT_* checks,
which ensures that PROT_NONE now works.

Reported-by: Shakeel Butt <shakeelb@google.com>

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michael Ellermen <mpe@ellerman.id.au>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Shuah Khan <shuah@kernel.org>
---

 b/arch/x86/include/asm/pkeys.h |   12 +++++++++++-
 b/arch/x86/mm/pkeys.c          |   19 ++++++++++---------
 2 files changed, 21 insertions(+), 10 deletions(-)

diff -puN arch/x86/include/asm/pkeys.h~pkeys-abandon-exec-only-pkey-more-aggressively arch/x86/include/asm/pkeys.h
--- a/arch/x86/include/asm/pkeys.h~pkeys-abandon-exec-only-pkey-more-aggressively	2018-03-21 15:47:49.810198922 -0700
+++ b/arch/x86/include/asm/pkeys.h	2018-03-21 15:47:49.816198922 -0700
@@ -2,6 +2,8 @@
 #ifndef _ASM_X86_PKEYS_H
 #define _ASM_X86_PKEYS_H
 
+#define ARCH_DEFAULT_PKEY	0
+
 #define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1)
 
 extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
@@ -15,7 +17,7 @@ extern int __execute_only_pkey(struct mm
 static inline int execute_only_pkey(struct mm_struct *mm)
 {
 	if (!boot_cpu_has(X86_FEATURE_OSPKE))
-		return 0;
+		return ARCH_DEFAULT_PKEY;
 
 	return __execute_only_pkey(mm);
 }
@@ -56,6 +58,14 @@ bool mm_pkey_is_allocated(struct mm_stru
 		return false;
 	if (pkey >= arch_max_pkey())
 		return false;
+	/*
+	 * The exec-only pkey is set in the allocation map, but
+	 * is not available to any of the user interfaces like
+	 * mprotect_pkey().
+	 */
+	if (pkey == mm->context.execute_only_pkey)
+		return false;
+
 	return mm_pkey_allocation_map(mm) & (1U << pkey);
 }
 
diff -puN arch/x86/mm/pkeys.c~pkeys-abandon-exec-only-pkey-more-aggressively arch/x86/mm/pkeys.c
--- a/arch/x86/mm/pkeys.c~pkeys-abandon-exec-only-pkey-more-aggressively	2018-03-21 15:47:49.812198922 -0700
+++ b/arch/x86/mm/pkeys.c	2018-03-21 15:47:49.816198922 -0700
@@ -94,15 +94,7 @@ int __arch_override_mprotect_pkey(struct
 	 */
 	if (pkey != -1)
 		return pkey;
-	/*
-	 * Look for a protection-key-drive execute-only mapping
-	 * which is now being given permissions that are not
-	 * execute-only.  Move it back to the default pkey.
-	 */
-	if (vma_is_pkey_exec_only(vma) &&
-	    (prot & (PROT_READ|PROT_WRITE))) {
-		return 0;
-	}
+
 	/*
 	 * The mapping is execute-only.  Go try to get the
 	 * execute-only protection key.  If we fail to do that,
@@ -113,7 +105,16 @@ int __arch_override_mprotect_pkey(struct
 		pkey = execute_only_pkey(vma->vm_mm);
 		if (pkey > 0)
 			return pkey;
+	} else if (vma_is_pkey_exec_only(vma)) {
+		/*
+		 * Protections are *not* PROT_EXEC, but the mapping
+		 * is using the exec-only pkey.  This mapping was
+		 * PROT_EXEC and will no longer be.  Move back to
+		 * the default pkey.
+		 */
+		return ARCH_DEFAULT_PKEY;
 	}
+
 	/*
 	 * This is a vanilla, non-pkey mprotect (or we failed to
 	 * setup execute-only), inherit the pkey from the VMA we
_

  parent reply	other threads:[~2018-03-23 18:12 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-23 18:09 [PATCH 0/9] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-03-23 18:09 ` [PATCH 1/9] x86, pkeys: do not special case protection key 0 Dave Hansen
2018-03-26 17:35   ` Ram Pai
2018-03-26 17:39     ` Dave Hansen
2018-03-27  2:27   ` Ram Pai
2018-03-27  4:11     ` Dave Hansen
2018-03-23 18:09 ` [PATCH 2/9] x86, pkeys, selftests: save off 'prot' for allocations Dave Hansen
2018-03-23 18:09 ` [PATCH 3/9] x86, pkeys, selftests: add a test for pkey 0 Dave Hansen
2018-03-23 18:09 ` Dave Hansen [this message]
2018-03-23 19:15   ` [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC Shakeel Butt
2018-03-23 19:23     ` Dave Hansen
2018-03-23 19:27       ` Shakeel Butt
2018-03-23 19:29         ` Dave Hansen
2018-03-23 19:38       ` Thomas Gleixner
2018-03-23 19:45         ` Thomas Gleixner
2018-03-23 19:48           ` Dave Hansen
2018-03-23 18:09 ` [PATCH 5/9] x86, pkeys, selftests: fix pointer math Dave Hansen
2018-03-23 18:09 ` [PATCH 6/9] x86, pkeys, selftests: fix pkey exhaustion test off-by-one Dave Hansen
2018-03-23 18:09 ` [PATCH 7/9] x86, pkeys, selftests: factor out "instruction page" Dave Hansen
2018-03-23 18:09 ` [PATCH 8/9] x86, pkeys, selftests: add allow faults on unknown keys Dave Hansen
2018-03-23 18:09 ` [PATCH 9/9] x86, pkeys, selftests: add PROT_EXEC test Dave Hansen
2018-03-26 17:27 [PATCH 0/9] [v2] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-03-26 17:27 ` [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC Dave Hansen
2018-04-07  0:09   ` Ram Pai
2018-04-07  0:47     ` Dave Hansen
2018-04-07  1:09       ` Ram Pai
2018-04-26 17:57         ` Dave Hansen
2018-04-30  7:51           ` Ram Pai
2018-04-30 16:36             ` Dave Hansen
2018-04-25 22:10   ` Shakeel Butt
2018-04-26  8:55     ` Thomas Gleixner
2018-04-26 18:17       ` Dave Hansen
2018-04-27 17:45 [PATCH 0/9] [v3] x86, pkeys: two protection keys bug fixes Dave Hansen
2018-04-27 17:45 ` [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC Dave Hansen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180323180911.E43ACAB8@viggo.jf.intel.com \
    --to=dave.hansen@linux.intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=dave.hansen@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linuxram@us.ibm.com \
    --cc=mingo@kernel.org \
    --cc=mpe@ellerman.id.au \
    --cc=shakeelb@google.com \
    --cc=shuah@kernel.org \
    --cc=tglx@linutronix.de \
    --subject='Re: [PATCH 4/9] x86, pkeys: override pkey when moving away from PROT_EXEC' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).