The patch titled
Subject: mm, kasan, kmsan: copy_from/to_kernel_nofault
has been added to the -mm mm-unstable branch. Its filename is
mm-kasan-kmsan-copy_from-to_kernel_nofault.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kasan-kmsan-copy_from-to_kernel_nofault.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
Subject: mm, kasan, kmsan: copy_from/to_kernel_nofault
Date: Sat, 5 Oct 2024 21:48:13 +0500
Instrument copy_from_kernel_nofault() with KMSAN for uninitialized kernel
memory check and copy_to_kernel_nofault() with KASAN, KCSAN to detect the
memory corruption.
syzbot reported that bpf_probe_read_kernel() kernel helper triggered KASAN
report via kasan_check_range() which is not the expected behaviour as
copy_from_kernel_nofault() is meant to be a non-faulting helper.
Solution is, suggested by Marco Elver, to replace KASAN, KCSAN check in
copy_from_kernel_nofault() with KMSAN detection of copying uninitilaized
kernel memory. In copy_to_kernel_nofault() we can retain
instrument_write() for the memory corruption instrumentation but before
pagefault_disable().
copy_to_kernel_nofault() is tested on x86_64 and arm64 with
CONFIG_KASAN_SW_TAGS. On arm64 with CONFIG_KASAN_HW_TAGS, kunit test
currently fails. Need more clarification on it - currently, disabled in
kunit test.
Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@xxxxxxxxxxxxxx/
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20241005164813.2475778-2-snovitoll@xxxxxxxxx
Suggested-by: Marco Elver <elver@xxxxxxxxxx>
Reported-by: syzbot+61123a5daeb9f7454599@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++
mm/kmsan/kmsan_test.c | 17 +++++++++++++++++
mm/maccess.c | 7 +++++--
3 files changed, 49 insertions(+), 2 deletions(-)
--- a/mm/kasan/kasan_test_c.c~mm-kasan-kmsan-copy_from-to_kernel_nofault
+++ a/mm/kasan/kasan_test_c.c
@@ -1954,6 +1954,32 @@ static void rust_uaf(struct kunit *test)
KUNIT_EXPECT_KASAN_FAIL(test, kasan_test_rust_uaf());
}
+static void copy_to_kernel_nofault_oob(struct kunit *test)
+{
+ char *ptr;
+ char buf[128];
+ size_t size = sizeof(buf);
+
+ /* Not detecting fails currently with HW_TAGS */
+ KASAN_TEST_NEEDS_CONFIG_OFF(test, CONFIG_KASAN_HW_TAGS);
+
+ ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+ OPTIMIZER_HIDE_VAR(ptr);
+
+ if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) {
+ /* Check that the returned pointer is tagged. */
+ KUNIT_EXPECT_GE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_MIN);
+ KUNIT_EXPECT_LT(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
+ }
+
+ KUNIT_EXPECT_KASAN_FAIL(test,
+ copy_to_kernel_nofault(&buf[0], ptr, size));
+ KUNIT_EXPECT_KASAN_FAIL(test,
+ copy_to_kernel_nofault(ptr, &buf[0], size));
+ kfree(ptr);
+}
+
static struct kunit_case kasan_kunit_test_cases[] = {
KUNIT_CASE(kmalloc_oob_right),
KUNIT_CASE(kmalloc_oob_left),
@@ -2027,6 +2053,7 @@ static struct kunit_case kasan_kunit_tes
KUNIT_CASE(match_all_not_assigned),
KUNIT_CASE(match_all_ptr_tag),
KUNIT_CASE(match_all_mem_tag),
+ KUNIT_CASE(copy_to_kernel_nofault_oob),
KUNIT_CASE(rust_uaf),
{}
};
--- a/mm/kmsan/kmsan_test.c~mm-kasan-kmsan-copy_from-to_kernel_nofault
+++ a/mm/kmsan/kmsan_test.c
@@ -640,6 +640,22 @@ static void test_unpoison_memory(struct
KUNIT_EXPECT_TRUE(test, report_matches(&expect));
}
+static void test_copy_from_kernel_nofault(struct kunit *test)
+{
+ long ret;
+ char buf[4], src[4];
+ size_t size = sizeof(buf);
+
+ EXPECTATION_UNINIT_VALUE_FN(expect, "copy_from_kernel_nofault");
+ kunit_info(
+ test,
+ "testing copy_from_kernel_nofault with uninitialized memory\n");
+
+ ret = copy_from_kernel_nofault((char *)&buf[0], (char *)&src[0], size);
+ USE(ret);
+ KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
static struct kunit_case kmsan_test_cases[] = {
KUNIT_CASE(test_uninit_kmalloc),
KUNIT_CASE(test_init_kmalloc),
@@ -664,6 +680,7 @@ static struct kunit_case kmsan_test_case
KUNIT_CASE(test_long_origin_chain),
KUNIT_CASE(test_stackdepot_roundtrip),
KUNIT_CASE(test_unpoison_memory),
+ KUNIT_CASE(test_copy_from_kernel_nofault),
{},
};
--- a/mm/maccess.c~mm-kasan-kmsan-copy_from-to_kernel_nofault
+++ a/mm/maccess.c
@@ -15,7 +15,7 @@ bool __weak copy_from_kernel_nofault_all
#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) { \
- __get_kernel_nofault(dst, src, type, err_label); \
+ __get_kernel_nofault(dst, src, type, err_label); \
dst += sizeof(type); \
src += sizeof(type); \
len -= sizeof(type); \
@@ -31,6 +31,8 @@ long copy_from_kernel_nofault(void *dst,
if (!copy_from_kernel_nofault_allowed(src, size))
return -ERANGE;
+ /* Make sure uninitialized kernel memory isn't copied. */
+ kmsan_check_memory(src, size);
pagefault_disable();
if (!(align & 7))
copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
@@ -49,7 +51,7 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofau
#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) { \
- __put_kernel_nofault(dst, src, type, err_label); \
+ __put_kernel_nofault(dst, src, type, err_label); \
dst += sizeof(type); \
src += sizeof(type); \
len -= sizeof(type); \
@@ -62,6 +64,7 @@ long copy_to_kernel_nofault(void *dst, c
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
align = (unsigned long)dst | (unsigned long)src;
+ instrument_write(dst, size);
pagefault_disable();
if (!(align & 7))
copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
_
Patches currently in -mm which might be from snovitoll@xxxxxxxxx are
mm-kasan-kmsan-copy_from-to_kernel_nofault.patch
