linux-kernel - [tip:x86/pti] x86/entry/32: Add debug code to check entry/exit CR3

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Thu, 19 Jul 2018 16:38:52 -0700
From:   tip-bot for Joerg Roedel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     dvlasenk@...hat.com, boris.ostrovsky@...cle.com,
        David.Laight@...lab.com, llong@...hat.com, luto@...nel.org,
        hpa@...or.com, jroedel@...e.de, peterz@...radead.org, pavel@....cz,
        eduval@...zon.com, aarcange@...hat.com, jpoimboe@...hat.com,
        jgross@...e.com, mingo@...nel.org, bp@...en8.de,
        torvalds@...ux-foundation.org, brgerst@...il.com,
        dhgutteridge@...patico.ca, linux-kernel@...r.kernel.org,
        will.deacon@....com, dave.hansen@...el.com, jkosina@...e.cz,
        tglx@...utronix.de, gregkh@...uxfoundation.org
Subject: [tip:x86/pti] x86/entry/32: Add debug code to check entry/exit CR3

Commit-ID:  97193702c6d353e12aefc0fb2f73a98ca421cd56
Gitweb:     https://git.kernel.org/tip/97193702c6d353e12aefc0fb2f73a98ca421cd56
Author:     Joerg Roedel <jroedel@...e.de>
AuthorDate: Wed, 18 Jul 2018 11:41:16 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 20 Jul 2018 01:11:49 +0200

x86/entry/32: Add debug code to check entry/exit CR3

Add code to check whether the kernel is entered and left with the correct
CR3 and make it depend on CONFIG_DEBUG_ENTRY.  This is needed because there
is no NX protection of user-addresses in the kernel-CR3 on x86-32 and that
type of bug would not be detected otherwise.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Pavel Machek <pavel@....cz>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: linux-mm@...ck.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Laight <David.Laight@...lab.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Will Deacon <will.deacon@....com>
Cc: aliguori@...zon.com
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Waiman Long <llong@...hat.com>
Cc: "David H . Gutteridge" <dhgutteridge@...patico.ca>
Cc: joro@...tes.org
Link: https://lkml.kernel.org/r/1531906876-13451-40-git-send-email-joro@8bytes.org

---
 arch/x86/entry/entry_32.S | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index b1541c74c71a..010cdb41e3c7 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -166,6 +166,24 @@
 .Lend_\@:
 .endm
 
+.macro BUG_IF_WRONG_CR3 no_user_check=0
+#ifdef CONFIG_DEBUG_ENTRY
+	ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+	.if \no_user_check == 0
+	/* coming from usermode? */
+	testl	$SEGMENT_RPL_MASK, PT_CS(%esp)
+	jz	.Lend_\@
+	.endif
+	/* On user-cr3? */
+	movl	%cr3, %eax
+	testl	$PTI_SWITCH_MASK, %eax
+	jnz	.Lend_\@
+	/* From userspace with kernel cr3 - BUG */
+	ud2
+.Lend_\@:
+#endif
+.endm
+
 /*
  * Switch to kernel cr3 if not already loaded and return current cr3 in
  * \scratch_reg
@@ -213,6 +231,8 @@
 .macro SAVE_ALL_NMI cr3_reg:req
 	SAVE_ALL
 
+	BUG_IF_WRONG_CR3
+
 	/*
 	 * Now switch the CR3 when PTI is enabled.
 	 *
@@ -224,6 +244,7 @@
 
 .Lend_\@:
 .endm
+
 /*
  * This is a sneaky trick to help the unwinder find pt_regs on the stack.  The
  * frame pointer is replaced with an encoded pointer to pt_regs.  The encoding
@@ -287,6 +308,8 @@
 
 .Lswitched_\@:
 
+	BUG_IF_WRONG_CR3
+
 	RESTORE_REGS pop=\pop
 .endm
 
@@ -357,6 +380,8 @@
 
 	ALTERNATIVE     "", "jmp .Lend_\@", X86_FEATURE_XENPV
 
+	BUG_IF_WRONG_CR3
+
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
 
 	/*
@@ -799,6 +824,7 @@ ENTRY(entry_SYSENTER_32)
 	 */
 	pushfl
 	pushl	%eax
+	BUG_IF_WRONG_CR3 no_user_check=1
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
 	popl	%eax
 	popfl
@@ -893,6 +919,7 @@ ENTRY(entry_SYSENTER_32)
 	 * whereas POPF does not.)
 	 */
 	btrl	$X86_EFLAGS_IF_BIT, (%esp)
+	BUG_IF_WRONG_CR3 no_user_check=1
 	popfl
 	popl	%eax
 
@@ -970,6 +997,8 @@ restore_all:
 	/* Switch back to user CR3 */
 	SWITCH_TO_USER_CR3 scratch_reg=%eax
 
+	BUG_IF_WRONG_CR3
+
 	/* Restore user state */
 	RESTORE_REGS pop=4			# skip orig_eax/error_code
 .Lirq_return:
@@ -983,6 +1012,7 @@ restore_all:
 restore_all_kernel:
 	TRACE_IRQS_IRET
 	PARANOID_EXIT_TO_KERNEL_MODE
+	BUG_IF_WRONG_CR3
 	RESTORE_REGS 4
 	jmp	.Lirq_return
 
@@ -990,6 +1020,19 @@ restore_all_kernel:
 ENTRY(iret_exc	)
 	pushl	$0				# no error code
 	pushl	$do_iret_error
+
+#ifdef CONFIG_DEBUG_ENTRY
+	/*
+	 * The stack-frame here is the one that iret faulted on, so its a
+	 * return-to-user frame. We are on kernel-cr3 because we come here from
+	 * the fixup code. This confuses the CR3 checker, so switch to user-cr3
+	 * as the checker expects it.
+	 */
+	pushl	%eax
+	SWITCH_TO_USER_CR3 scratch_reg=%eax
+	popl	%eax
+#endif
+
 	jmp	common_exception
 .previous
 	_ASM_EXTABLE(.Lirq_return, iret_exc)