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Subject[PATCH 12/31] 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 | 59 ++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 58 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 9693485..b5ef003 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -328,6 +328,25 @@
#endif /* CONFIG_X86_ESPFIX32 */
.endm

+/* 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
+
+/* Unconditionally switch to kernel cr3 */
+.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI
+ movl %cr3, \scratch_reg
+ andl $(~PTI_SWITCH_MASK), \scratch_reg
+ movl \scratch_reg, %cr3
+.Lend_\@:
+.endm
+

/*
* Called with pt_regs fully populated and kernel segments loaded,
@@ -343,6 +362,8 @@

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

+ SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
+
/* 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
@@ -637,6 +658,18 @@ 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:
@@ -691,6 +724,10 @@ ENTRY(entry_SYSENTER_32)
movl PT_OLDESP(%esp), %ecx /* pt_regs->sp */
1: mov PT_FS(%esp), %fs
PTGS_TO_GS
+
+ /* Segments are restored - switch to user cr3 */
+ SWITCH_TO_USER_CR3 scratch_reg=%eax
+
popl %ebx /* pt_regs->bx */
addl $2*4, %esp /* skip pt_regs->cx and pt_regs->dx */
popl %esi /* pt_regs->si */
@@ -778,7 +815,23 @@ restore_all:
.Lrestore_all_notrace:
CHECK_AND_APPLY_ESPFIX
.Lrestore_nocheck:
- RESTORE_REGS 4 # skip orig_eax/error_code
+ /*
+ * First restore user segments. This can cause exceptions, so we
+ * run it with kernel cr3.
+ */
+ RESTORE_SEGMENTS
+
+ /*
+ * Segments are restored - no more exceptions from here on except on
+ * iret, but that handled safely.
+ */
+ SWITCH_TO_USER_CR3 scratch_reg=%eax
+
+ /* Restore rest */
+ RESTORE_INT_REGS
+
+ /* Unwind stack to the iret frame */
+ RESTORE_SKIP_SEGMENTS 4 # skip orig_eax/error_code
.Lirq_return:
INTERRUPT_RETURN

@@ -1139,6 +1192,10 @@ ENTRY(debug)

SAVE_ALL
ENCODE_FRAME_POINTER
+
+ /* Make sure we are running on kernel cr3 */
+ SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
+
xorl %edx, %edx # error code 0
movl %esp, %eax # pt_regs pointer

--
2.7.4
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