x86/speculation: Use IBRS if available before calling into firmware

Retpoline means the kernel is safe because it has no indirect branches.
But firmware isn't, so use IBRS for firmware calls if it's available.

Block preemption while IBRS is set, although in practice the call sites
already had to be doing that.

Ignore hpwdt.c for now. It's taking spinlocks and calling into firmware
code, from an NMI handler. I don't want to touch that with a bargepole.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: arjan.van.de.ven@intel.com
Cc: bp@alien8.de
Cc: dave.hansen@intel.com
Cc: jmattson@google.com
Cc: karahmed@amazon.de
Cc: kvm@vger.kernel.org
Cc: pbonzini@redhat.com
Cc: rkrcmar@redhat.com
Link: http://lkml.kernel.org/r/1519037457-7643-2-git-send-email-dwmw@amazon.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/apm.h b/arch/x86/include/asm/apm.h
index 4d4015ddcf2633e9e8388216f9e9c8639e2eced8..c356098b6fb92b8ff7d42b2fd813c2a8551d3db1 100644 (file)
--- 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/nospec-branch.h>
+
 #ifdef APM_ZERO_SEGS
 #      define APM_DO_ZERO_SEGS \
                "pushl %%ds\n\t" \
@@ -32,6 +34,7 @@ static inline void apm_bios_call_asm(u32 func, u32 ebx_in, u32 ecx_in,
         * N.B. We do NOT need a cld after the BIOS call
         * because we always save and restore the flags.
         */
+       firmware_restrict_branch_speculation_start();
        __asm__ __volatile__(APM_DO_ZERO_SEGS
                "pushl %%edi\n\t"
                "pushl %%ebp\n\t"
@@ -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");
+       firmware_restrict_branch_speculation_end();
 }
 
 static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in,
@@ -56,6 +60,7 @@ static inline bool apm_bios_call_simple_asm(u32 func, u32 ebx_in,
         * N.B. We do NOT need a cld after the BIOS call
         * because we always save and restore the flags.
         */
+       firmware_restrict_branch_speculation_start();
        __asm__ __volatile__(APM_DO_ZERO_SEGS
                "pushl %%edi\n\t"
                "pushl %%ebp\n\t"
@@ -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");
+       firmware_restrict_branch_speculation_end();
        return error;
 }
 

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 0dfe4d3f74e24d6655fc40f0460b9e489fb9ef69..f41079da38c55f8a2e891b044ac9ffb73919c37e 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -213,6 +213,7 @@
 #define X86_FEATURE_SEV                        ( 7*32+20) /* AMD Secure Encrypted Virtualization */
 
 #define X86_FEATURE_USE_IBPB           ( 7*32+21) /* "" Indirect Branch Prediction Barrier enabled */
+#define X86_FEATURE_USE_IBRS_FW                ( 7*32+22) /* "" Use IBRS during runtime firmware calls */
 
 /* Virtualization flags: Linux defined, word 8 */
 #define X86_FEATURE_TPR_SHADOW         ( 8*32+ 0) /* Intel TPR Shadow */

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 85f6ccb80b91771029f347f1875f7a6d923ef184..a399c1ebf6f0e6d974da0b773248b9c0cfe811a9 100644 (file)
--- 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/nospec-branch.h>
 
 /*
  * We map the EFI regions needed for runtime services non-contiguously,
@@ -36,8 +37,18 @@
 
 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();                                             \
+       firmware_restrict_branch_speculation_start();                   \
+})
+
+#define arch_efi_call_virt_teardown()                                  \
+({                                                                     \
+       firmware_restrict_branch_speculation_end();                     \
+       kernel_fpu_end();                                               \
+})
+
 
 /*
  * Wrap all the virtual calls in a way that forces the parameters on the stack.
@@ -73,6 +84,7 @@ struct efi_scratch {
        efi_sync_low_kernel_mappings();                                 \
        preempt_disable();                                              \
        __kernel_fpu_begin();                                           \
+       firmware_restrict_branch_speculation_start();                   \
                                                                        \
        if (efi_scratch.use_pgd) {                                      \
                efi_scratch.prev_cr3 = __read_cr3();                    \
@@ -91,6 +103,7 @@ struct efi_scratch {
                __flush_tlb_all();                                      \
        }                                                               \
                                                                        \
+       firmware_restrict_branch_speculation_end();                     \
        __kernel_fpu_end();                                             \
        preempt_enable();                                               \
 })

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index af34b1e8069a10e9ff0f2ad9fd896e5018fb8eb3..ec90c3228991231289f4c008ac0d866e02d07c0b 100644 (file)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -219,17 +219,38 @@ static inline void vmexit_fill_RSB(void)
 #endif
 }
 
+#define alternative_msr_write(_msr, _val, _feature)            \
+       asm volatile(ALTERNATIVE("",                            \
+                                "movl %[msr], %%ecx\n\t"       \
+                                "movl %[val], %%eax\n\t"       \
+                                "movl $0, %%edx\n\t"           \
+                                "wrmsr",                       \
+                                _feature)                      \
+                    : : [msr] "i" (_msr), [val] "i" (_val)     \
+                    : "eax", "ecx", "edx", "memory")
+
 static inline void indirect_branch_prediction_barrier(void)
 {
-       asm volatile(ALTERNATIVE("",
-                                "movl %[msr], %%ecx\n\t"
-                                "movl %[val], %%eax\n\t"
-                                "movl $0, %%edx\n\t"
-                                "wrmsr",
-                                X86_FEATURE_USE_IBPB)
-                    : : [msr] "i" (MSR_IA32_PRED_CMD),
-                        [val] "i" (PRED_CMD_IBPB)
-                    : "eax", "ecx", "edx", "memory");
+       alternative_msr_write(MSR_IA32_PRED_CMD, PRED_CMD_IBPB,
+                             X86_FEATURE_USE_IBPB);
+}
+
+/*
+ * With retpoline, we must use IBRS to restrict branch prediction
+ * before calling into firmware.
+ */
+static inline void firmware_restrict_branch_speculation_start(void)
+{
+       preempt_disable();
+       alternative_msr_write(MSR_IA32_SPEC_CTRL, SPEC_CTRL_IBRS,
+                             X86_FEATURE_USE_IBRS_FW);
+}
+
+static inline void firmware_restrict_branch_speculation_end(void)
+{
+       alternative_msr_write(MSR_IA32_SPEC_CTRL, 0,
+                             X86_FEATURE_USE_IBRS_FW);
+       preempt_enable();
 }
 
 #endif /* __ASSEMBLY__ */

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d71c8b54b696d4593ffb15ff894468ad3e524a50..bfca937bdcc36ce8d9523f03dcc92e93d3c39d5c 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -300,6 +300,15 @@ retpoline_auto:
                setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
                pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
        }
+
+       /*
+        * Retpoline means the kernel is safe because it has no indirect
+        * branches. But firmware isn't, so use IBRS to protect that.
+        */
+       if (boot_cpu_has(X86_FEATURE_IBRS)) {
+               setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
+               pr_info("Enabling Restricted Speculation for firmware calls\n");
+       }
 }
 
 #undef pr_fmt
@@ -326,8 +335,9 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, c
        if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2))
                return sprintf(buf, "Not affected\n");
 
-       return sprintf(buf, "%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
+       return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],
                       boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",
+                      boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",
                       spectre_v2_module_string());
 }
 #endif