Merge tag 'x86_bugs_for_v6.5_rc6' of git://git.kernel.org/pub/scm/lin…

…ux/kernel/git/tip/tip Pull x86 mitigation fixes from Borislav Petkov: "The first set of fallout fixes after the embargo madness. There will be another set next week too. - A first series of cleanups/unifications and documentation improvements to the SRSO and GDS mitigations code which got postponed to after the embargo date - Fix the SRSO aliasing addresses assertion so that the LLVM linker can parse it too" * tag 'x86_bugs_for_v6.5_rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: driver core: cpu: Fix the fallback cpu_show_gds() name x86: Move gds_ucode_mitigated() declaration to header x86/speculation: Add cpu_show_gds() prototype driver core: cpu: Make cpu_show_not_affected() static x86/srso: Fix build breakage with the LLVM linker Documentation/srso: Document IBPB aspect and fix formatting driver core: cpu: Unify redundant silly stubs Documentation/hw-vuln: Unify filename specification in index
openbmc · Aug 12, 2023 · 272b86b · 272b86b
2 parents f8de32c + 3477144
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diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst
@@ -13,11 +13,11 @@ are configurable at compile, boot or run time.
    l1tf
    mds
    tsx_async_abort
-   multihit.rst
-   special-register-buffer-data-sampling.rst
-   core-scheduling.rst
-   l1d_flush.rst
-   processor_mmio_stale_data.rst
-   cross-thread-rsb.rst
+   multihit
+   special-register-buffer-data-sampling
+   core-scheduling
+   l1d_flush
+   processor_mmio_stale_data
+   cross-thread-rsb
    srso
-   gather_data_sampling.rst
+   gather_data_sampling
diff --git a/Documentation/admin-guide/hw-vuln/srso.rst b/Documentation/admin-guide/hw-vuln/srso.rst
@@ -42,42 +42,59 @@ The sysfs file showing SRSO mitigation status is:
 
 The possible values in this file are:
 
- - 'Not affected'               The processor is not vulnerable
+ * 'Not affected':
 
- - 'Vulnerable: no microcode'   The processor is vulnerable, no
-                                microcode extending IBPB functionality
-                                to address the vulnerability has been
-                                applied.
+   The processor is not vulnerable
 
- - 'Mitigation: microcode'      Extended IBPB functionality microcode
-                                patch has been applied. It does not
-                                address User->Kernel and Guest->Host
-                                transitions protection but it does
-                                address User->User and VM->VM attack
-                                vectors.
+ * 'Vulnerable: no microcode':
 
-                                (spec_rstack_overflow=microcode)
+   The processor is vulnerable, no microcode extending IBPB
+   functionality to address the vulnerability has been applied.
 
- - 'Mitigation: safe RET'       Software-only mitigation. It complements
-                                the extended IBPB microcode patch
-                                functionality by addressing User->Kernel 
-                                and Guest->Host transitions protection.
+ * 'Mitigation: microcode':
 
-                                Selected by default or by
-                                spec_rstack_overflow=safe-ret
+   Extended IBPB functionality microcode patch has been applied. It does
+   not address User->Kernel and Guest->Host transitions protection but it
+   does address User->User and VM->VM attack vectors.
 
- - 'Mitigation: IBPB'           Similar protection as "safe RET" above
-                                but employs an IBPB barrier on privilege
-                                domain crossings (User->Kernel,
-                                Guest->Host).
+   Note that User->User mitigation is controlled by how the IBPB aspect in
+   the Spectre v2 mitigation is selected:
 
-                                (spec_rstack_overflow=ibpb)
+    * conditional IBPB:
+
+      where each process can select whether it needs an IBPB issued
+      around it PR_SPEC_DISABLE/_ENABLE etc, see :doc:`spectre`
+
+    * strict:
+
+      i.e., always on - by supplying spectre_v2_user=on on the kernel
+      command line
+
+   (spec_rstack_overflow=microcode)
+
+ * 'Mitigation: safe RET':
+
+   Software-only mitigation. It complements the extended IBPB microcode
+   patch functionality by addressing User->Kernel and Guest->Host
+   transitions protection.
+
+   Selected by default or by spec_rstack_overflow=safe-ret
+
+ * 'Mitigation: IBPB':
+
+   Similar protection as "safe RET" above but employs an IBPB barrier on
+   privilege domain crossings (User->Kernel, Guest->Host).
+
+  (spec_rstack_overflow=ibpb)
+
+ * 'Mitigation: IBPB on VMEXIT':
+
+   Mitigation addressing the cloud provider scenario - the Guest->Host
+   transitions only.
+
+   (spec_rstack_overflow=ibpb-vmexit)
 
- - 'Mitigation: IBPB on VMEXIT' Mitigation addressing the cloud provider
-                                scenario - the Guest->Host transitions
-                                only.
 
-                                (spec_rstack_overflow=ibpb-vmexit)
 
 In order to exploit vulnerability, an attacker needs to:
 

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
@@ -731,4 +731,6 @@ bool arch_is_platform_page(u64 paddr);
 #define arch_is_platform_page arch_is_platform_page
 #endif
 
+extern bool gds_ucode_mitigated(void);
+
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
@@ -529,11 +529,17 @@ INIT_PER_CPU(irq_stack_backing_store);
 
 #ifdef CONFIG_CPU_SRSO
 /*
- * GNU ld cannot do XOR so do: (A | B) - (A & B) in order to compute the XOR
+ * GNU ld cannot do XOR until 2.41.
+ * https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=f6f78318fca803c4907fb8d7f6ded8295f1947b1
+ *
+ * LLVM lld cannot do XOR until lld-17.
+ * https://github.com/llvm/llvm-project/commit/fae96104d4378166cbe5c875ef8ed808a356f3fb
+ *
+ * Instead do: (A | B) - (A & B) in order to compute the XOR
  * of the two function addresses:
  */
-. = ASSERT(((srso_untrain_ret_alias | srso_safe_ret_alias) -
-		(srso_untrain_ret_alias & srso_safe_ret_alias)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)),
+. = ASSERT(((ABSOLUTE(srso_untrain_ret_alias) | srso_safe_ret_alias) -
+		(ABSOLUTE(srso_untrain_ret_alias) & srso_safe_ret_alias)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)),
 		"SRSO function pair won't alias");
 #endif
 

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
@@ -314,8 +314,6 @@ u64 __read_mostly host_xcr0;
 
 static struct kmem_cache *x86_emulator_cache;
 
-extern bool gds_ucode_mitigated(void);
-
 /*
  * When called, it means the previous get/set msr reached an invalid msr.
  * Return true if we want to ignore/silent this failed msr access.

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
@@ -509,85 +509,30 @@ static void __init cpu_dev_register_generic(void)
 }
 
 #ifdef CONFIG_GENERIC_CPU_VULNERABILITIES
-
-ssize_t __weak cpu_show_meltdown(struct device *dev,
-				 struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_spectre_v1(struct device *dev,
-				   struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_spectre_v2(struct device *dev,
-				   struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_spec_store_bypass(struct device *dev,
-					  struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_l1tf(struct device *dev,
-			     struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_mds(struct device *dev,
-			    struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_tsx_async_abort(struct device *dev,
-					struct device_attribute *attr,
-					char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_itlb_multihit(struct device *dev,
-				      struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_srbds(struct device *dev,
+static ssize_t cpu_show_not_affected(struct device *dev,
 			      struct device_attribute *attr, char *buf)
 {
 	return sysfs_emit(buf, "Not affected\n");
 }
 
-ssize_t __weak cpu_show_mmio_stale_data(struct device *dev,
-					struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_retbleed(struct device *dev,
-				 struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_spec_rstack_overflow(struct device *dev,
-					     struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
-
-ssize_t __weak cpu_show_gds(struct device *dev,
-			    struct device_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "Not affected\n");
-}
+#define CPU_SHOW_VULN_FALLBACK(func)					\
+	ssize_t cpu_show_##func(struct device *,			\
+				  struct device_attribute *, char *)	\
+		 __attribute__((weak, alias("cpu_show_not_affected")))
+
+CPU_SHOW_VULN_FALLBACK(meltdown);
+CPU_SHOW_VULN_FALLBACK(spectre_v1);
+CPU_SHOW_VULN_FALLBACK(spectre_v2);
+CPU_SHOW_VULN_FALLBACK(spec_store_bypass);
+CPU_SHOW_VULN_FALLBACK(l1tf);
+CPU_SHOW_VULN_FALLBACK(mds);
+CPU_SHOW_VULN_FALLBACK(tsx_async_abort);
+CPU_SHOW_VULN_FALLBACK(itlb_multihit);
+CPU_SHOW_VULN_FALLBACK(srbds);
+CPU_SHOW_VULN_FALLBACK(mmio_stale_data);
+CPU_SHOW_VULN_FALLBACK(retbleed);
+CPU_SHOW_VULN_FALLBACK(spec_rstack_overflow);
+CPU_SHOW_VULN_FALLBACK(gds);
 
 static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
 static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
@@ -72,6 +72,8 @@ extern ssize_t cpu_show_retbleed(struct device *dev,
 				 struct device_attribute *attr, char *buf);
 extern ssize_t cpu_show_spec_rstack_overflow(struct device *dev,
 					     struct device_attribute *attr, char *buf);
+extern ssize_t cpu_show_gds(struct device *dev,
+			    struct device_attribute *attr, char *buf);
 
 extern __printf(4, 5)
 struct device *cpu_device_create(struct device *parent, void *drvdata,