Merge tag 'x86-urgent-2023-09-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc x86 fixes from Ingo Molnar:

 - Fix a kexec bug

 - Fix an UML build bug

 - Fix a handful of SRSO related bugs

 - Fix a shadow stacks handling bug & robustify related code

* tag 'x86-urgent-2023-09-22' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/shstk: Add warning for shadow stack double unmap
  x86/shstk: Remove useless clone error handling
  x86/shstk: Handle vfork clone failure correctly
  x86/srso: Fix SBPB enablement for spec_rstack_overflow=off
  x86/srso: Don't probe microcode in a guest
  x86/srso: Set CPUID feature bits independently of bug or mitigation status
  x86/srso: Fix srso_show_state() side effect
  x86/asm: Fix build of UML with KASAN
  x86/mm, kexec, ima: Use memblock_free_late() from ima_free_kexec_buffer()

Author: torvalds

arch/x86/include/asm/linkage.h

@@ -105,6 +105,13 @@
 	CFI_POST_PADDING					\
 	SYM_FUNC_END(__cfi_##name)
 
+/* UML needs to be able to override memcpy() and friends for KASAN. */
+#ifdef CONFIG_UML
+# define SYM_FUNC_ALIAS_MEMFUNC	SYM_FUNC_ALIAS_WEAK
+#else
+# define SYM_FUNC_ALIAS_MEMFUNC	SYM_FUNC_ALIAS
+#endif
+
 /* SYM_TYPED_FUNC_START -- use for indirectly called globals, w/ CFI type */
 #define SYM_TYPED_FUNC_START(name)				\
 	SYM_TYPED_START(name, SYM_L_GLOBAL, SYM_F_ALIGN)	\

arch/x86/include/asm/mmu_context.h

@@ -186,8 +186,7 @@ do {						\
 #else
 #define deactivate_mm(tsk, mm)			\
 do {						\
-	if (!tsk->vfork_done)			\
-		shstk_free(tsk);		\
+	shstk_free(tsk);			\
 	load_gs_index(0);			\
 	loadsegment(fs, 0);			\
 } while (0)

arch/x86/include/asm/processor.h

@@ -683,13 +683,11 @@ extern u16 get_llc_id(unsigned int cpu);
 #ifdef CONFIG_CPU_SUP_AMD
 extern u32 amd_get_nodes_per_socket(void);
 extern u32 amd_get_highest_perf(void);
-extern bool cpu_has_ibpb_brtype_microcode(void);
 extern void amd_clear_divider(void);
 extern void amd_check_microcode(void);
 #else
 static inline u32 amd_get_nodes_per_socket(void)	{ return 0; }
 static inline u32 amd_get_highest_perf(void)		{ return 0; }
-static inline bool cpu_has_ibpb_brtype_microcode(void)	{ return false; }
 static inline void amd_clear_divider(void)		{ }
 static inline void amd_check_microcode(void)		{ }
 #endif

arch/x86/kernel/cpu/amd.c

@@ -766,6 +766,15 @@ static void early_init_amd(struct cpuinfo_x86 *c)
 
 	if (cpu_has(c, X86_FEATURE_TOPOEXT))
 		smp_num_siblings = ((cpuid_ebx(0x8000001e) >> 8) & 0xff) + 1;
+
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_IBPB_BRTYPE)) {
+		if (c->x86 == 0x17 && boot_cpu_has(X86_FEATURE_AMD_IBPB))
+			setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE);
+		else if (c->x86 >= 0x19 && !wrmsrl_safe(MSR_IA32_PRED_CMD, PRED_CMD_SBPB)) {
+			setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE);
+			setup_force_cpu_cap(X86_FEATURE_SBPB);
+		}
+	}
 }
 
 static void init_amd_k8(struct cpuinfo_x86 *c)
@@ -1301,25 +1310,6 @@ void amd_check_microcode(void)
 	on_each_cpu(zenbleed_check_cpu, NULL, 1);
 }
 
-bool cpu_has_ibpb_brtype_microcode(void)
-{
-	switch (boot_cpu_data.x86) {
-	/* Zen1/2 IBPB flushes branch type predictions too. */
-	case 0x17:
-		return boot_cpu_has(X86_FEATURE_AMD_IBPB);
-	case 0x19:
-		/* Poke the MSR bit on Zen3/4 to check its presence. */
-		if (!wrmsrl_safe(MSR_IA32_PRED_CMD, PRED_CMD_SBPB)) {
-			setup_force_cpu_cap(X86_FEATURE_SBPB);
-			return true;
-		} else {
-			return false;
-		}
-	default:
-		return false;
-	}
-}
-
 /*
  * Issue a DIV 0/1 insn to clear any division data from previous DIV
  * operations.

arch/x86/kernel/cpu/bugs.c

@@ -2404,26 +2404,15 @@ early_param("spec_rstack_overflow", srso_parse_cmdline);
 
 static void __init srso_select_mitigation(void)
 {
-	bool has_microcode;
+	bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
 
 	if (!boot_cpu_has_bug(X86_BUG_SRSO) || cpu_mitigations_off())
 		goto pred_cmd;
 
-	/*
-	 * The first check is for the kernel running as a guest in order
-	 * for guests to verify whether IBPB is a viable mitigation.
-	 */
-	has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) || cpu_has_ibpb_brtype_microcode();
 	if (!has_microcode) {
 		pr_warn("IBPB-extending microcode not applied!\n");
 		pr_warn(SRSO_NOTICE);
 	} else {
-		/*
-		 * Enable the synthetic (even if in a real CPUID leaf)
-		 * flags for guests.
-		 */
-		setup_force_cpu_cap(X86_FEATURE_IBPB_BRTYPE);
-
 		/*
 		 * Zen1/2 with SMT off aren't vulnerable after the right
 		 * IBPB microcode has been applied.
@@ -2444,7 +2433,7 @@ static void __init srso_select_mitigation(void)
 
 	switch (srso_cmd) {
 	case SRSO_CMD_OFF:
-		return;
+		goto pred_cmd;
 
 	case SRSO_CMD_MICROCODE:
 		if (has_microcode) {
@@ -2717,7 +2706,7 @@ static ssize_t srso_show_state(char *buf)
 
 	return sysfs_emit(buf, "%s%s\n",
 			  srso_strings[srso_mitigation],
-			  (cpu_has_ibpb_brtype_microcode() ? "" : ", no microcode"));
+			  boot_cpu_has(X86_FEATURE_IBPB_BRTYPE) ? "" : ", no microcode");
 }
 
 static ssize_t gds_show_state(char *buf)

arch/x86/kernel/process.c

@@ -257,13 +257,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
 		io_bitmap_share(p);
 
-	/*
-	 * If copy_thread() if failing, don't leak the shadow stack possibly
-	 * allocated in shstk_alloc_thread_stack() above.
-	 */
-	if (ret)
-		shstk_free(p);
-
 	return ret;
 }
 

arch/x86/kernel/setup.c

@@ -358,15 +358,11 @@ static void __init add_early_ima_buffer(u64 phys_addr)
 #if defined(CONFIG_HAVE_IMA_KEXEC) && !defined(CONFIG_OF_FLATTREE)
 int __init ima_free_kexec_buffer(void)
 {
-	int rc;
-
 	if (!ima_kexec_buffer_size)
 		return -ENOENT;
 
-	rc = memblock_phys_free(ima_kexec_buffer_phys,
-				ima_kexec_buffer_size);
-	if (rc)
-		return rc;
+	memblock_free_late(ima_kexec_buffer_phys,
+			   ima_kexec_buffer_size);
 
 	ima_kexec_buffer_phys = 0;
 	ima_kexec_buffer_size = 0;

arch/x86/kernel/shstk.c

@@ -205,10 +205,21 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk, unsigned long cl
 		return 0;
 
 	/*
-	 * For CLONE_VM, except vfork, the child needs a separate shadow
+	 * For CLONE_VFORK the child will share the parents shadow stack.
+	 * Make sure to clear the internal tracking of the thread shadow
+	 * stack so the freeing logic run for child knows to leave it alone.
+	 */
+	if (clone_flags & CLONE_VFORK) {
+		shstk->base = 0;
+		shstk->size = 0;
+		return 0;
+	}
+
+	/*
+	 * For !CLONE_VM the child will use a copy of the parents shadow
 	 * stack.
 	 */
-	if ((clone_flags & (CLONE_VFORK | CLONE_VM)) != CLONE_VM)
+	if (!(clone_flags & CLONE_VM))
 		return 0;
 
 	size = adjust_shstk_size(stack_size);
@@ -408,7 +419,25 @@ void shstk_free(struct task_struct *tsk)
 	if (!tsk->mm || tsk->mm != current->mm)
 		return;
 
+	/*
+	 * If shstk->base is NULL, then this task is not managing its
+	 * own shadow stack (CLONE_VFORK). So skip freeing it.
+	 */
+	if (!shstk->base)
+		return;
+
+	/*
+	 * shstk->base is NULL for CLONE_VFORK child tasks, and so is
+	 * normal. But size = 0 on a shstk->base is not normal and
+	 * indicated an attempt to free the thread shadow stack twice.
+	 * Warn about it.
+	 */
+	if (WARN_ON(!shstk->size))
+		return;
+
 	unmap_shadow_stack(shstk->base, shstk->size);
+
+	shstk->size = 0;
 }
 
 static int wrss_control(bool enable)

arch/x86/lib/memcpy_64.S

@@ -40,7 +40,7 @@ SYM_TYPED_FUNC_START(__memcpy)
 SYM_FUNC_END(__memcpy)
 EXPORT_SYMBOL(__memcpy)
 
-SYM_FUNC_ALIAS(memcpy, __memcpy)
+SYM_FUNC_ALIAS_MEMFUNC(memcpy, __memcpy)
 EXPORT_SYMBOL(memcpy)
 
 SYM_FUNC_START_LOCAL(memcpy_orig)

arch/x86/lib/memmove_64.S

@@ -212,5 +212,5 @@ SYM_FUNC_START(__memmove)
 SYM_FUNC_END(__memmove)
 EXPORT_SYMBOL(__memmove)
 
-SYM_FUNC_ALIAS(memmove, __memmove)
+SYM_FUNC_ALIAS_MEMFUNC(memmove, __memmove)
 EXPORT_SYMBOL(memmove)