From: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
commit 2dbb887e875b1de3ca8f40ddf26bcfe55798c609 upstream.
Implement Kernel IBRS - currently the only known option to mitigate RSB
underflow speculation issues on Skylake hardware.
Note: since IBRS_ENTER requires fuller context established than
UNTRAIN_RET, it must be placed after it. However, since UNTRAIN_RET
itself implies a RET, it must come after IBRS_ENTER. This means
IBRS_ENTER needs to also move UNTRAIN_RET.
Note 2: KERNEL_IBRS is sub-optimal for XenPV.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
[cascardo: conflict at arch/x86/entry/entry_64_compat.S]
[cascardo: conflict fixups, no ANNOTATE_NOENDBR]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[ bp: Adjust context ]
Signed-off-by: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
---
arch/x86/entry/calling.h | 58 ++++++++++++++++++++++++++++++
arch/x86/entry/entry_64.S | 33 +++++++++++++++++
arch/x86/entry/entry_64_compat.S | 12 ++++++-
arch/x86/include/asm/cpufeatures.h | 2 +-
4 files changed, 103 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 273b562af8fa..ef759951fd0f 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -6,6 +6,8 @@
#include <asm/percpu.h>
#include <asm/asm-offsets.h>
#include <asm/processor-flags.h>
+#include <asm/msr.h>
+#include <asm/nospec-branch.h>
/*
@@ -328,6 +330,62 @@ For 32-bit we have the following conventions - kernel is built with
#endif
+/*
+ * IBRS kernel mitigation for Spectre_v2.
+ *
+ * Assumes full context is established (PUSH_REGS, CR3 and GS) and it clobbers
+ * the regs it uses (AX, CX, DX). Must be called before the first RET
+ * instruction (NOTE! UNTRAIN_RET includes a RET instruction)
+ *
+ * The optional argument is used to save/restore the current value,
+ * which is used on the paranoid paths.
+ *
+ * Assumes x86_spec_ctrl_{base,current} to have SPEC_CTRL_IBRS set.
+ */
+.macro IBRS_ENTER save_reg
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+ movl $MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+ rdmsr
+ shl $32, %rdx
+ or %rdx, %rax
+ mov %rax, \save_reg
+ test $SPEC_CTRL_IBRS, %eax
+ jz .Ldo_wrmsr_\@
+ lfence
+ jmp .Lend_\@
+.Ldo_wrmsr_\@:
+.endif
+
+ movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+ movl %edx, %eax
+ shr $32, %rdx
+ wrmsr
+.Lend_\@:
+.endm
+
+/*
+ * Similar to IBRS_ENTER, requires KERNEL GS,CR3 and clobbers (AX, CX, DX)
+ * regs. Must be called after the last RET.
+ */
+.macro IBRS_EXIT save_reg
+ ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_KERNEL_IBRS
+ movl $MSR_IA32_SPEC_CTRL, %ecx
+
+.ifnb \save_reg
+ mov \save_reg, %rdx
+.else
+ movq PER_CPU_VAR(x86_spec_ctrl_current), %rdx
+ andl $(~SPEC_CTRL_IBRS), %edx
+.endif
+
+ movl %edx, %eax
+ shr $32, %rdx
+ wrmsr
+.Lend_\@:
+.endm
+
/*
* Mitigate Spectre v1 for conditional swapgs code paths.
*
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d3472e773b5a..fee102f5a7d5 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -230,6 +230,10 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
/* IRQs are off. */
movq %rsp, %rdi
+
+ /* clobbers %rax, make sure it is after saving the syscall nr */
+ IBRS_ENTER
+
call do_syscall_64 /* returns with IRQs disabled */
TRACE_IRQS_IRETQ /* we're about to change IF */
@@ -301,6 +305,7 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
* perf profiles. Nothing jumps here.
*/
syscall_return_via_sysret:
+ IBRS_EXIT
POP_REGS pop_rdi=0
/*
@@ -590,6 +595,7 @@ GLOBAL(retint_user)
TRACE_IRQS_IRETQ
GLOBAL(swapgs_restore_regs_and_return_to_usermode)
+ IBRS_EXIT
#ifdef CONFIG_DEBUG_ENTRY
/* Assert that pt_regs indicates user mode. */
testb $3, CS(%rsp)
@@ -1133,6 +1139,9 @@ idtentry machine_check do_mce has_error_code=0 paranoid=1
* Save all registers in pt_regs, and switch gs if needed.
* Use slow, but surefire "are we in kernel?" check.
* Return: ebx=0: need swapgs on exit, ebx=1: otherwise
+ *
+ * R14 - old CR3
+ * R15 - old SPEC_CTRL
*/
ENTRY(paranoid_entry)
UNWIND_HINT_FUNC
@@ -1156,6 +1165,12 @@ ENTRY(paranoid_entry)
*/
FENCE_SWAPGS_KERNEL_ENTRY
+ /*
+ * Once we have CR3 and %GS setup save and set SPEC_CTRL. Just like
+ * CR3 above, keep the old value in a callee saved register.
+ */
+ IBRS_ENTER save_reg=%r15
+
ret
END(paranoid_entry)
@@ -1170,9 +1185,19 @@ END(paranoid_entry)
* to try to handle preemption here.
*
* On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it)
+ *
+ * R14 - old CR3
+ * R15 - old SPEC_CTRL
*/
ENTRY(paranoid_exit)
UNWIND_HINT_REGS
+
+ /*
+ * Must restore IBRS state before both CR3 and %GS since we need access
+ * to the per-CPU x86_spec_ctrl_shadow variable.
+ */
+ IBRS_EXIT save_reg=%r15
+
DISABLE_INTERRUPTS(CLBR_ANY)
TRACE_IRQS_OFF_DEBUG
testl %ebx, %ebx /* swapgs needed? */
@@ -1207,8 +1232,10 @@ ENTRY(error_entry)
FENCE_SWAPGS_USER_ENTRY
/* We have user CR3. Change to kernel CR3. */
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
+ IBRS_ENTER
.Lerror_entry_from_usermode_after_swapgs:
+
/* Put us onto the real thread stack. */
popq %r12 /* save return addr in %12 */
movq %rsp, %rdi /* arg0 = pt_regs pointer */
@@ -1271,6 +1298,7 @@ ENTRY(error_entry)
SWAPGS
FENCE_SWAPGS_USER_ENTRY
SWITCH_TO_KERNEL_CR3 scratch_reg=%rax
+ IBRS_ENTER
/*
* Pretend that the exception came from user mode: set up pt_regs
@@ -1376,6 +1404,8 @@ ENTRY(nmi)
PUSH_AND_CLEAR_REGS rdx=(%rdx)
ENCODE_FRAME_POINTER
+ IBRS_ENTER
+
/*
* At this point we no longer need to worry about stack damage
* due to nesting -- we're on the normal thread stack and we're
@@ -1599,6 +1629,9 @@ end_repeat_nmi:
movq $-1, %rsi
call do_nmi
+ /* Always restore stashed SPEC_CTRL value (see paranoid_entry) */
+ IBRS_EXIT save_reg=%r15
+
RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
testl %ebx, %ebx /* swapgs needed? */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 304e3daf82dd..8cdc3af68c53 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -4,7 +4,6 @@
*
* Copyright 2000-2002 Andi Kleen, SuSE Labs.
*/
-#include "calling.h"
#include <asm/asm-offsets.h>
#include <asm/current.h>
#include <asm/errno.h>
@@ -17,6 +16,8 @@
#include <linux/linkage.h>
#include <linux/err.h>
+#include "calling.h"
+
.section .entry.text, "ax"
/*
@@ -106,6 +107,8 @@ ENTRY(entry_SYSENTER_compat)
xorl %r15d, %r15d /* nospec r15 */
cld
+ IBRS_ENTER
+
/*
* SYSENTER doesn't filter flags, so we need to clear NT and AC
* ourselves. To save a few cycles, we can check whether
@@ -250,6 +253,8 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
*/
TRACE_IRQS_OFF
+ IBRS_ENTER
+
movq %rsp, %rdi
call do_fast_syscall_32
/* XEN PV guests always use IRET path */
@@ -259,6 +264,9 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe)
/* Opportunistic SYSRET */
sysret32_from_system_call:
TRACE_IRQS_ON /* User mode traces as IRQs on. */
+
+ IBRS_EXIT
+
movq RBX(%rsp), %rbx /* pt_regs->rbx */
movq RBP(%rsp), %rbp /* pt_regs->rbp */
movq EFLAGS(%rsp), %r11 /* pt_regs->flags (in r11) */
@@ -385,6 +393,8 @@ ENTRY(entry_INT80_compat)
*/
TRACE_IRQS_OFF
+ IBRS_ENTER
+
movq %rsp, %rdi
call do_int80_syscall_32
.Lsyscall_32_done:
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 2e96129ed68b..b78acf1e70b6 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -202,7 +202,7 @@
#define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface */
#define X86_FEATURE_SME ( 7*32+10) /* AMD Secure Memory Encryption */
#define X86_FEATURE_PTI ( 7*32+11) /* Kernel Page Table Isolation enabled */
-/* FREE! ( 7*32+12) */
+#define X86_FEATURE_KERNEL_IBRS ( 7*32+12) /* "" Set/clear IBRS on kernel entry/exit */
/* FREE! ( 7*32+13) */
#define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory Number */
#define X86_FEATURE_CDP_L2 ( 7*32+15) /* Code and Data Prioritization L2 */
--
2.17.1
