[PATCH 5/7] x86: Use IBRS for firmware update path

Tim Chen
2018-01-04T18:18:11Z

From: David Woodhouse <dwmw@amazon.co.uk>

We are impervious to the indirect branch prediction attack with retpoline
but firmware won't be, so we still need to set IBRS to protect
firmware code execution when calling into firmware at runtime.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
---
arch/x86/include/asm/apm.h | 6 ++++++
arch/x86/include/asm/efi.h | 16 ++++++++++++++--
arch/x86/include/asm/spec_ctrl.h | 37 +++++++++++++++++++++++++++++++++++++
3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/apm.h b/arch/x86/include/asm/apm.h
index 4d4015d..1ca4f7b 100644
--- a/arch/x86/include/asm/apm.h
+++ b/arch/x86/include/asm/apm.h
@@ -7,6 +7,8 @@
#ifndef _ASM_X86_MACH_DEFAULT_APM_H
#define _ASM_X86_MACH_DEFAULT_APM_H

+#include <asm/spec_ctrl.h>
+
#ifdef APM_ZERO_SEGS
# define APM_DO_ZERO_SEGS \
"pushl %%ds\n\t" \
@@ -28,6 +30,7 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in,
u32 *eax, u32 *ebx, u32 *ecx,
u32 *edx, u32 *esi)
{
+ unprotected_firmware_begin();
/*
* N.B. We do NOT need a cld after the BIOS call
* because we always save and restore the flags.
@@ -44,6 +47,7 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in,
"=S" (*esi)
: "a" (func), "b" (ebx_in), "c" (ecx_in)
: "memory", "cc");
+ unprotected_formware_end();
}

static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in,
@@ -52,6 +56,7 @@ static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in,
int cx, dx, si;
bool error;

+ unprotected_firmware_begin();
/*
* N.B. We do NOT need a cld after the BIOS call
* because we always save and restore the flags.
@@ -68,6 +73,7 @@ static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in,
"=S" (si)
: "a" (func), "b" (ebx_in), "c" (ecx_in)
: "memory", "cc");
+ unprotected_formware_end();
return error;
}

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 85f6ccb..25bd506 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -6,6 +6,7 @@
#include <asm/pgtable.h>
#include <asm/processor-flags.h>
#include <asm/tlb.h>
+#include <asm/spec_ctrl.h>

/*
* We map the EFI regions needed for runtime services non-contiguously,
@@ -36,8 +37,17 @@

extern asmlinkage unsigned long efi_call_phys(void *, ...);

-#define arch_efi_call_virt_setup() kernel_fpu_begin()
-#define arch_efi_call_virt_teardown() kernel_fpu_end()
+#define arch_efi_call_virt_setup() \
+{( \
+ kernel_fpu_begin(); \
+ unprotected_firmware_begin(); \
+)}
+
+#define arch_efi_call_virt_teardown() \
+{( \
+ unprotected_firmware_end(); \
+ kernel_fpu_end(); \
+)}

/*
* Wrap all the virtual calls in a way that forces the parameters on the stack.
@@ -73,6 +83,7 @@ struct efi_scratch {
efi_sync_low_kernel_mappings(); \
preempt_disable(); \
__kernel_fpu_begin(); \
+ unprotected_firmware_begin(); \
\
if (efi_scratch.use_pgd) { \
efi_scratch.prev_cr3 = __read_cr3(); \
@@ -91,6 +102,7 @@ struct efi_scratch {
__flush_tlb_all(); \
} \
\
+ unprotected_firmware_end(); \
__kernel_fpu_end(); \
preempt_enable(); \
})
diff --git a/arch/x86/include/asm/spec_ctrl.h b/arch/x86/include/asm/spec_ctrl.h
index 28b0314..23b2804 100644
--- a/arch/x86/include/asm/spec_ctrl.h
+++ b/arch/x86/include/asm/spec_ctrl.h
@@ -113,5 +113,42 @@ static inline void unprotected_speculation_end(void)
rmb();
}

+
+#if defined(RETPOLINE)
+/*
+ * RETPOLINE does not protect against indirect speculation
+ * in firmware code. Enable IBRS to protect firmware execution.
+ */
+static inline void unprotected_firmware_begin(void)
+{
+ if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+ __disable_indirect_speculation();
+ else
+ /*
+ * If we intended to disable indirect speculation
+ * but come here due to mis-speculation, we need
+ * to stop the mis-speculation with rmb.
+ */
+ rmb();
+}
+
+static inline void unprotected_firmware_end(void)
+{
+ if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
+ __enable_indirect_speculation();
+}
+
+#else
+static inline void unprotected_firmware_begin(void)
+{
+ return;
+}
+
+static inline void unprotected_firmware_end(void)
+{
+ return;
+}
+#endif
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_SPEC_CTRL_H */
--
2.9.4