The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: 895429076512e9d1cf5428181076299c90713159
Gitweb: https://git.kernel.org/tip/895429076512e9d1cf5428181076299c90713159
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 20 Nov 2019 15:02:26 +01:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 21 Nov 2019 19:37:44 +01:00
x86/entry/32: Fix NMI vs ESPFIX
When the NMI lands on an ESPFIX_SS, we are on the entry stack and must
swizzle, otherwise we'll run do_nmi() on the entry stack, which is
BAD.
Also, similar to the normal exception path, we need to correct the
ESPFIX magic before leaving the entry stack, otherwise pt_regs will
present a non-flat stack pointer.
Tested by running sigreturn_32 concurrent with perf-record.
Fixes: e5862d0515ad ("x86/entry/32: Leave the kernel via trampoline stack")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
arch/x86/entry/entry_32.S | 53 +++++++++++++++++++++++++++++---------
1 file changed, 41 insertions(+), 12 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 647e2a2..0b8c931 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -205,6 +205,7 @@
#define CS_FROM_ENTRY_STACK (1 << 31)
#define CS_FROM_USER_CR3 (1 << 30)
#define CS_FROM_KERNEL (1 << 29)
+#define CS_FROM_ESPFIX (1 << 28)
.macro FIXUP_FRAME
/*
@@ -342,8 +343,8 @@
.endif
.endm
-.macro SAVE_ALL_NMI cr3_reg:req
- SAVE_ALL
+.macro SAVE_ALL_NMI cr3_reg:req unwind_espfix=0
+ SAVE_ALL unwind_espfix=\unwind_espfix
BUG_IF_WRONG_CR3
@@ -1526,6 +1527,10 @@ ENTRY(nmi)
ASM_CLAC
#ifdef CONFIG_X86_ESPFIX32
+ /*
+ * ESPFIX_SS is only ever set on the return to user path
+ * after we've switched to the entry stack.
+ */
pushl %eax
movl %ss, %eax
cmpw $__ESPFIX_SS, %ax
@@ -1561,6 +1566,11 @@ ENTRY(nmi)
movl %ebx, %esp
.Lnmi_return:
+#ifdef CONFIG_X86_ESPFIX32
+ testl $CS_FROM_ESPFIX, PT_CS(%esp)
+ jnz .Lnmi_from_espfix
+#endif
+
CHECK_AND_APPLY_ESPFIX
RESTORE_ALL_NMI cr3_reg=%edi pop=4
jmp .Lirq_return
@@ -1568,23 +1578,42 @@ ENTRY(nmi)
#ifdef CONFIG_X86_ESPFIX32
.Lnmi_espfix_stack:
/*
- * create the pointer to lss back
+ * Create the pointer to LSS back
*/
pushl %ss
pushl %esp
addl $4, (%esp)
- /* copy the iret frame of 12 bytes */
- .rept 3
- pushl 16(%esp)
- .endr
- pushl %eax
- SAVE_ALL_NMI cr3_reg=%edi
+
+ /* Copy the (short) IRET frame */
+ pushl 4*4(%esp) # flags
+ pushl 4*4(%esp) # cs
+ pushl 4*4(%esp) # ip
+
+ pushl %eax # orig_ax
+
+ SAVE_ALL_NMI cr3_reg=%edi unwind_espfix=1
ENCODE_FRAME_POINTER
- FIXUP_ESPFIX_STACK # %eax == %esp
+
+ /* clear CS_FROM_KERNEL, set CS_FROM_ESPFIX */
+ xorl $(CS_FROM_ESPFIX | CS_FROM_KERNEL), PT_CS(%esp)
+
xorl %edx, %edx # zero error code
- call do_nmi
+ movl %esp, %eax # pt_regs pointer
+ jmp .Lnmi_from_sysenter_stack
+
+.Lnmi_from_espfix:
RESTORE_ALL_NMI cr3_reg=%edi
- lss 12+4(%esp), %esp # back to espfix stack
+ /*
+ * Because we cleared CS_FROM_KERNEL, IRET_FRAME 'forgot' to
+ * fix up the gap and long frame:
+ *
+ * 3 - original frame (exception)
+ * 2 - ESPFIX block (above)
+ * 6 - gap (FIXUP_FRAME)
+ * 5 - long frame (FIXUP_FRAME)
+ * 1 - orig_ax
+ */
+ lss (1+5+6)*4(%esp), %esp # back to espfix stack
jmp .Lirq_return
#endif
END(nmi)
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