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Date: Sat, 24 Feb 2024 18:42:43 -0800
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Subject: Re: [syzbot] Re: [syzbot] [virtualization?] KMSAN: uninit-value in
 virtqueue_add (4)
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Subject: Re: [syzbot] [virtualization?] KMSAN: uninit-value in virtqueue_add (4)
Author: penguin-kernel@i-love.sakura.ne.jp

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git v6.7

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index cc6b8e087192..f13bba3a9dab 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -58,7 +58,16 @@ static inline void clear_page(void *page)
 			   : "cc", "memory", "rax", "rcx");
 }
 
+#ifdef CONFIG_KMSAN
+/* Use of non-instrumented assembly version confuses KMSAN. */
+void *memcpy(void *to, const void *from, __kernel_size_t len);
+static inline void copy_page(void *to, void *from)
+{
+	memcpy(to, from, PAGE_SIZE);
+}
+#else
 void copy_page(void *to, void *from);
+#endif
 
 #ifdef CONFIG_X86_5LEVEL
 /*
diff --git a/arch/x86/lib/copy_mc.c b/arch/x86/lib/copy_mc.c
index 6e8b7e600def..bc701dcbb133 100644
--- a/arch/x86/lib/copy_mc.c
+++ b/arch/x86/lib/copy_mc.c
@@ -61,9 +61,9 @@ unsigned long copy_mc_enhanced_fast_string(void *dst, const void *src, unsigned
  */
 unsigned long __must_check copy_mc_to_kernel(void *dst, const void *src, unsigned len)
 {
-	if (copy_mc_fragile_enabled)
+	if (0 && copy_mc_fragile_enabled)
 		return copy_mc_fragile(dst, src, len);
-	if (static_cpu_has(X86_FEATURE_ERMS))
+	if (0 && static_cpu_has(X86_FEATURE_ERMS))
 		return copy_mc_enhanced_fast_string(dst, src, len);
 	memcpy(dst, src, len);
 	return 0;
@@ -74,14 +74,14 @@ unsigned long __must_check copy_mc_to_user(void __user *dst, const void *src, un
 {
 	unsigned long ret;
 
-	if (copy_mc_fragile_enabled) {
+	if (0 && copy_mc_fragile_enabled) {
 		__uaccess_begin();
 		ret = copy_mc_fragile((__force void *)dst, src, len);
 		__uaccess_end();
 		return ret;
 	}
 
-	if (static_cpu_has(X86_FEATURE_ERMS)) {
+	if (0 && static_cpu_has(X86_FEATURE_ERMS)) {
 		__uaccess_begin();
 		ret = copy_mc_enhanced_fast_string((__force void *)dst, src, len);
 		__uaccess_end();
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index e0aa6b440ca5..039ffa49f324 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -253,11 +253,16 @@ size_t memcpy_from_iter_mc(void *iter_from, size_t progress,
 
 static size_t __copy_from_iter_mc(void *addr, size_t bytes, struct iov_iter *i)
 {
+	size_t ret;
+
 	if (unlikely(i->count < bytes))
 		bytes = i->count;
 	if (unlikely(!bytes))
 		return 0;
-	return iterate_bvec(i, bytes, addr, NULL, memcpy_from_iter_mc);
+	ret = iterate_bvec(i, bytes, addr, NULL, memcpy_from_iter_mc);
+	if (bytes != ret)
+		printk("addr=%px bytes=%d ret=%d\n", addr, bytes, ret);
+	return ret;
 }
 
 static __always_inline
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 5d6e2dee5692..0b09daa188ef 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -359,6 +359,12 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
 }
 
 /* Functions from kmsan-checks.h follow. */
+
+/*
+ * To create an origin, kmsan_poison_memory() unwinds the stacks and stores it
+ * into the stack depot. This may cause deadlocks if done from within KMSAN
+ * runtime, therefore we bail out if kmsan_in_runtime().
+ */
 void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
 {
 	if (!kmsan_enabled || kmsan_in_runtime())
@@ -371,47 +377,31 @@ void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
 }
 EXPORT_SYMBOL(kmsan_poison_memory);
 
+/*
+ * Unlike kmsan_poison_memory(), this function can be used from within KMSAN
+ * runtime, because it does not trigger allocations or call instrumented code.
+ */
 void kmsan_unpoison_memory(const void *address, size_t size)
 {
 	unsigned long ua_flags;
 
-	if (!kmsan_enabled || kmsan_in_runtime())
+	if (!kmsan_enabled)
 		return;
 
 	ua_flags = user_access_save();
-	kmsan_enter_runtime();
 	/* The users may want to poison/unpoison random memory. */
 	kmsan_internal_unpoison_memory((void *)address, size,
 				       KMSAN_POISON_NOCHECK);
-	kmsan_leave_runtime();
 	user_access_restore(ua_flags);
 }
 EXPORT_SYMBOL(kmsan_unpoison_memory);
 
 /*
- * Version of kmsan_unpoison_memory() that can be called from within the KMSAN
- * runtime.
- *
- * Non-instrumented IRQ entry functions receive struct pt_regs from assembly
- * code. Those regs need to be unpoisoned, otherwise using them will result in
- * false positives.
- * Using kmsan_unpoison_memory() is not an option in entry code, because the
- * return value of in_task() is inconsistent - as a result, certain calls to
- * kmsan_unpoison_memory() are ignored. kmsan_unpoison_entry_regs() ensures that
- * the registers are unpoisoned even if kmsan_in_runtime() is true in the early
- * entry code.
+ * Version of kmsan_unpoison_memory() called from IRQ entry functions.
  */
 void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
 {
-	unsigned long ua_flags;
-
-	if (!kmsan_enabled)
-		return;
-
-	ua_flags = user_access_save();
-	kmsan_internal_unpoison_memory((void *)regs, sizeof(*regs),
-				       KMSAN_POISON_NOCHECK);
-	user_access_restore(ua_flags);
+	kmsan_unpoison_memory((void *)regs, sizeof(*regs));
 }
 
 void kmsan_check_memory(const void *addr, size_t size)