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-rw-r--r--arch/x86/entry/calling.h17
-rw-r--r--arch/x86/entry/entry_64.S21
2 files changed, 35 insertions, 3 deletions
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 830bd984182b..515c0ceeb4a3 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -314,6 +314,23 @@ For 32-bit we have the following conventions - kernel is built with
#endif
+/*
+ * Mitigate Spectre v1 for conditional swapgs code paths.
+ *
+ * FENCE_SWAPGS_USER_ENTRY is used in the user entry swapgs code path, to
+ * prevent a speculative swapgs when coming from kernel space.
+ *
+ * FENCE_SWAPGS_KERNEL_ENTRY is used in the kernel entry non-swapgs code path,
+ * to prevent the swapgs from getting speculatively skipped when coming from
+ * user space.
+ */
+.macro FENCE_SWAPGS_USER_ENTRY
+ ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_USER
+.endm
+.macro FENCE_SWAPGS_KERNEL_ENTRY
+ ALTERNATIVE "", "lfence", X86_FEATURE_FENCE_SWAPGS_KERNEL
+.endm
+
.macro STACKLEAK_ERASE_NOCLOBBER
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
PUSH_AND_CLEAR_REGS
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 3f5a978a02a7..be9ca198c581 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -519,7 +519,7 @@ ENTRY(interrupt_entry)
testb $3, CS-ORIG_RAX+8(%rsp)
jz 1f
SWAPGS
-
+ FENCE_SWAPGS_USER_ENTRY
/*
* Switch to the thread stack. The IRET frame and orig_ax are
* on the stack, as well as the return address. RDI..R12 are
@@ -549,8 +549,10 @@ ENTRY(interrupt_entry)
UNWIND_HINT_FUNC
movq (%rdi), %rdi
+ jmp 2f
1:
-
+ FENCE_SWAPGS_KERNEL_ENTRY
+2:
PUSH_AND_CLEAR_REGS save_ret=1
ENCODE_FRAME_POINTER 8
@@ -1238,6 +1240,13 @@ ENTRY(paranoid_entry)
*/
SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg=%rax save_reg=%r14
+ /*
+ * The above SAVE_AND_SWITCH_TO_KERNEL_CR3 macro doesn't do an
+ * unconditional CR3 write, even in the PTI case. So do an lfence
+ * to prevent GS speculation, regardless of whether PTI is enabled.
+ */
+ FENCE_SWAPGS_KERNEL_ENTRY
+
ret
END(paranoid_entry)
@@ -1288,6 +1297,7 @@ ENTRY(error_entry)
* from user mode due to an IRET fault.
*/
SWAPGS
+ FENCE_SWAPGS_USER_ENTRY
/* We have user CR3. Change to kernel CR3. */
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
@@ -1301,6 +1311,8 @@ ENTRY(error_entry)
pushq %r12
ret
+.Lerror_entry_done_lfence:
+ FENCE_SWAPGS_KERNEL_ENTRY
.Lerror_entry_done:
ret
@@ -1318,7 +1330,7 @@ ENTRY(error_entry)
cmpq %rax, RIP+8(%rsp)
je .Lbstep_iret
cmpq $.Lgs_change, RIP+8(%rsp)
- jne .Lerror_entry_done
+ jne .Lerror_entry_done_lfence
/*
* hack: .Lgs_change can fail with user gsbase. If this happens, fix up
@@ -1326,6 +1338,7 @@ ENTRY(error_entry)
* .Lgs_change's error handler with kernel gsbase.
*/
SWAPGS
+ FENCE_SWAPGS_USER_ENTRY
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
jmp .Lerror_entry_done
@@ -1340,6 +1353,7 @@ ENTRY(error_entry)
* gsbase and CR3. Switch to kernel gsbase and CR3:
*/
SWAPGS
+ FENCE_SWAPGS_USER_ENTRY
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
/*
@@ -1431,6 +1445,7 @@ ENTRY(nmi)
swapgs
cld
+ FENCE_SWAPGS_USER_ENTRY
SWITCH_TO_KERNEL_CR3 scratch_reg=%rdx
movq %rsp, %rdx
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp