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Subject[PATCH 13/39] x86/entry/32: Add PTI cr3 switch to non-NMI entry/exit points
Date
From: Joerg Roedel <jroedel@suse.de>

Add unconditional cr3 switches between user and kernel cr3
to all non-NMI entry and exit points.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/entry/entry_32.S | 83 ++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 79 insertions(+), 4 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 9e06431..311aefa 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -154,6 +154,33 @@

#endif /* CONFIG_X86_32_LAZY_GS */

+/* Unconditionally switch to user cr3 */
+.macro SWITCH_TO_USER_CR3 scratch_reg:req
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+
+ movl %cr3, \scratch_reg
+ orl $PTI_SWITCH_MASK, \scratch_reg
+ movl \scratch_reg, %cr3
+.Lend_\@:
+.endm
+
+/*
+ * Switch to kernel cr3 if not already loaded and return current cr3 in
+ * \scratch_reg
+ */
+.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+ movl %cr3, \scratch_reg
+ /* Test if we are already on kernel CR3 */
+ testl $PTI_SWITCH_MASK, \scratch_reg
+ jz .Lend_\@
+ andl $(~PTI_SWITCH_MASK), \scratch_reg
+ movl \scratch_reg, %cr3
+ /* Return original CR3 in \scratch_reg */
+ orl $PTI_SWITCH_MASK, \scratch_reg
+.Lend_\@:
+.endm
+
.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0
cld
/* Push segment registers and %eax */
@@ -288,7 +315,6 @@
#endif /* CONFIG_X86_ESPFIX32 */
.endm

-
/*
* Called with pt_regs fully populated and kernel segments loaded,
* so we can access PER_CPU and use the integer registers.
@@ -301,11 +327,19 @@
*/

#define CS_FROM_ENTRY_STACK (1 << 31)
+#define CS_FROM_USER_CR3 (1 << 30)

.macro SWITCH_TO_KERNEL_STACK

ALTERNATIVE "", "jmp .Lend_\@", X86_FEATURE_XENPV

+ SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
+
+ /*
+ * %eax now contains the entry cr3 and we carry it forward in
+ * that register for the time this macro runs
+ */
+
/* Are we on the entry stack? Bail out if not! */
movl PER_CPU_VAR(cpu_entry_area), %edi
addl $CPU_ENTRY_AREA_entry_stack, %edi
@@ -374,7 +408,8 @@
* but switch back to the entry-stack again when we approach
* iret and return to the interrupted code-path. This usually
* happens when we hit an exception while restoring user-space
- * segment registers on the way back to user-space.
+ * segment registers on the way back to user-space or when the
+ * sysenter handler runs with eflags.tf set.
*
* When we switch to the task-stack here, we can't trust the
* contents of the entry-stack anymore, as the exception handler
@@ -391,6 +426,7 @@
*
* %esi: Entry-Stack pointer (same as %esp)
* %edi: Top of the task stack
+ * %eax: CR3 on kernel entry
*/

/* Calculate number of bytes on the entry stack in %ecx */
@@ -407,6 +443,14 @@
orl $CS_FROM_ENTRY_STACK, PT_CS(%esp)

/*
+ * Test the cr3 used to enter the kernel and add a marker
+ * so that we can switch back to it before iret.
+ */
+ testl $PTI_SWITCH_MASK, %eax
+ jz .Lcopy_pt_regs_\@
+ orl $CS_FROM_USER_CR3, PT_CS(%esp)
+
+ /*
* %esi and %edi are unchanged, %ecx contains the number of
* bytes to copy. The code at .Lcopy_pt_regs_\@ will allocate
* the stack-frame on task-stack and copy everything over
@@ -472,7 +516,7 @@

/*
* This macro handles the case when we return to kernel-mode on the iret
- * path and have to switch back to the entry stack.
+ * path and have to switch back to the entry stack and/or user-cr3
*
* See the comments below the .Lentry_from_kernel_\@ label in the
* SWITCH_TO_KERNEL_STACK macro for more details.
@@ -518,6 +562,18 @@
/* Safe to switch to entry-stack now */
movl %ebx, %esp

+ /*
+ * We came from entry-stack and need to check if we also need to
+ * switch back to user cr3.
+ */
+ testl $CS_FROM_USER_CR3, PT_CS(%esp)
+ jz .Lend_\@
+
+ /* Clear marker from stack-frame */
+ andl $(~CS_FROM_USER_CR3), PT_CS(%esp)
+
+ SWITCH_TO_USER_CR3 scratch_reg=%eax
+
.Lend_\@:
.endm
/*
@@ -711,6 +767,18 @@ ENTRY(xen_sysenter_target)
* 0(%ebp) arg6
*/
ENTRY(entry_SYSENTER_32)
+ /*
+ * On entry-stack with all userspace-regs live - save and
+ * restore eflags and %eax to use it as scratch-reg for the cr3
+ * switch.
+ */
+ pushfl
+ pushl %eax
+ SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
+ popl %eax
+ popfl
+
+ /* Stack empty again, switch to task stack */
movl TSS_entry_stack(%esp), %esp

.Lsysenter_past_esp:
@@ -791,6 +859,9 @@ ENTRY(entry_SYSENTER_32)
/* Switch to entry stack */
movl %eax, %esp

+ /* Now ready to switch the cr3 */
+ SWITCH_TO_USER_CR3 scratch_reg=%eax
+
/*
* Restore all flags except IF. (We restore IF separately because
* STI gives a one-instruction window in which we won't be interrupted,
@@ -871,7 +942,11 @@ restore_all:
.Lrestore_all_notrace:
CHECK_AND_APPLY_ESPFIX
.Lrestore_nocheck:
- RESTORE_REGS 4 # skip orig_eax/error_code
+ /* Switch back to user CR3 */
+ SWITCH_TO_USER_CR3 scratch_reg=%eax
+
+ /* Restore user state */
+ RESTORE_REGS pop=4 # skip orig_eax/error_code
.Lirq_return:
/*
* ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
--
2.7.4
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