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authorJoerg Roedel <jroedel@suse.de>2018-07-18 11:41:16 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-07-20 01:11:49 +0200
commit97193702c6d353e12aefc0fb2f73a98ca421cd56 (patch)
tree3712844784e0aebf5fcaeea48073c83605db3180 /arch/x86
parent5e8105950a8b3e03e805299b4d05020ee4eda31a (diff)
download96b-common-97193702c6d353e12aefc0fb2f73a98ca421cd56.tar.gz
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@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Pavel Machek <pavel@ucw.cz> Cc: "H . Peter Anvin" <hpa@zytor.com> Cc: linux-mm@kvack.org Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Juergen Gross <jgross@suse.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Jiri Kosina <jkosina@suse.cz> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com> Cc: Brian Gerst <brgerst@gmail.com> Cc: David Laight <David.Laight@aculab.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: Eduardo Valentin <eduval@amazon.com> Cc: Greg KH <gregkh@linuxfoundation.org> Cc: Will Deacon <will.deacon@arm.com> Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Waiman Long <llong@redhat.com> Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca> Cc: joro@8bytes.org Link: https://lkml.kernel.org/r/1531906876-13451-40-git-send-email-joro@8bytes.org
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/entry/entry_32.S43
1 files changed, 43 insertions, 0 deletions
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)