From 75cf0290271bf6dae9dee982aef15242dadf97e4 Mon Sep 17 00:00:00 2001
From: Alexander Potapenko <glider@google.com>
Date: Thu, 15 Sep 2022 17:03:52 +0200
Subject: instrumented.h: add KMSAN support

To avoid false positives, KMSAN needs to unpoison the data copied from the
userspace.  To detect infoleaks - check the memory buffer passed to
copy_to_user().

Link: https://lkml.kernel.org/r/20220915150417.722975-19-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/kmsan/hooks.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

(limited to 'mm/kmsan')

diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 6f3e64b0b61f..5c0eb25d984d 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -205,6 +205,44 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end)
 	kmsan_leave_runtime();
 }
 
+void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
+			size_t left)
+{
+	unsigned long ua_flags;
+
+	if (!kmsan_enabled || kmsan_in_runtime())
+		return;
+	/*
+	 * At this point we've copied the memory already. It's hard to check it
+	 * before copying, as the size of actually copied buffer is unknown.
+	 */
+
+	/* copy_to_user() may copy zero bytes. No need to check. */
+	if (!to_copy)
+		return;
+	/* Or maybe copy_to_user() failed to copy anything. */
+	if (to_copy <= left)
+		return;
+
+	ua_flags = user_access_save();
+	if ((u64)to < TASK_SIZE) {
+		/* This is a user memory access, check it. */
+		kmsan_internal_check_memory((void *)from, to_copy - left, to,
+					    REASON_COPY_TO_USER);
+	} else {
+		/* Otherwise this is a kernel memory access. This happens when a
+		 * compat syscall passes an argument allocated on the kernel
+		 * stack to a real syscall.
+		 * Don't check anything, just copy the shadow of the copied
+		 * bytes.
+		 */
+		kmsan_internal_memmove_metadata((void *)to, (void *)from,
+						to_copy - left);
+	}
+	user_access_restore(ua_flags);
+}
+EXPORT_SYMBOL(kmsan_copy_to_user);
+
 /* Functions from kmsan-checks.h follow. */
 void kmsan_poison_memory(const void *address, size_t size, gfp_t flags)
 {
-- 
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