diff mbox series

[v3] mm, kasan, kmsan: copy_from/to_kernel_nofault

Message ID 20241008101526.2591147-1-snovitoll@gmail.com (mailing list archive)
State New
Headers show
Series [v3] mm, kasan, kmsan: copy_from/to_kernel_nofault | expand

Commit Message

Sabyrzhan Tasbolatov Oct. 8, 2024, 10:15 a.m. UTC
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() explicitly for the memory corruption instrumentation.

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@mail.gmail.com/
Suggested-by: Marco Elver <elver@google.com>
Reported-by: syzbot+61123a5daeb9f7454599@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
---
v2:
- squashed previous submitted in -mm tree 2 patches based on Linus tree
v3:
- moved checks to *_nofault_loop macros per Marco's comments
- edited the commit message
---
 mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++
 mm/kmsan/kmsan_test.c   | 17 +++++++++++++++++
 mm/maccess.c            | 10 ++++++++--
 3 files changed, 52 insertions(+), 2 deletions(-)

Comments

Marco Elver Oct. 8, 2024, 11:35 a.m. UTC | #1
On Tue, 8 Oct 2024 at 12:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> wrote:
>
> 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() explicitly for the memory corruption instrumentation.
>
> 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.

I assume you retested. Did you also test the bpf_probe_read_kernel()
false positive no longer appears?

> Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@mail.gmail.com/
> Suggested-by: Marco Elver <elver@google.com>

This looks more reasonable:

Reviewed-by: Marco Elver <elver@google.com>

This looks like the most conservative thing to do for now.

> Reported-by: syzbot+61123a5daeb9f7454599@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
> Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
> v2:
> - squashed previous submitted in -mm tree 2 patches based on Linus tree
> v3:
> - moved checks to *_nofault_loop macros per Marco's comments
> - edited the commit message
> ---
>  mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++
>  mm/kmsan/kmsan_test.c   | 17 +++++++++++++++++
>  mm/maccess.c            | 10 ++++++++--
>  3 files changed, 52 insertions(+), 2 deletions(-)
>
> diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> index a181e4780d9d..5cff90f831db 100644
> --- a/mm/kasan/kasan_test_c.c
> +++ b/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_test_cases[] = {
>         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),
>         {}
>  };
> diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
> index 13236d579eba..9733a22c46c1 100644
> --- a/mm/kmsan/kmsan_test.c
> +++ b/mm/kmsan/kmsan_test.c
> @@ -640,6 +640,22 @@ static void test_unpoison_memory(struct kunit *test)
>         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_cases[] = {
>         KUNIT_CASE(test_long_origin_chain),
>         KUNIT_CASE(test_stackdepot_roundtrip),
>         KUNIT_CASE(test_unpoison_memory),
> +       KUNIT_CASE(test_copy_from_kernel_nofault),
>         {},
>  };
>
> diff --git a/mm/maccess.c b/mm/maccess.c
> index 518a25667323..3ca55ec63a6a 100644
> --- a/mm/maccess.c
> +++ b/mm/maccess.c
> @@ -13,9 +13,14 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
>         return true;
>  }
>
> +/*
> + * The below only uses kmsan_check_memory() to ensure uninitialized kernel
> + * memory isn't leaked.
> + */
>  #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);        \
> +               kmsan_check_memory(src, sizeof(type));                  \
>                 dst += sizeof(type);                                    \
>                 src += sizeof(type);                                    \
>                 len -= sizeof(type);                                    \
> @@ -49,7 +54,8 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
>
>  #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);        \
> +               instrument_write(dst, sizeof(type));                    \
>                 dst += sizeof(type);                                    \
>                 src += sizeof(type);                                    \
>                 len -= sizeof(type);                                    \
> --
> 2.34.1
>
Sabyrzhan Tasbolatov Oct. 8, 2024, 7:39 p.m. UTC | #2
On Tue, Oct 8, 2024 at 4:36 PM Marco Elver <elver@google.com> wrote:
>
> On Tue, 8 Oct 2024 at 12:14, Sabyrzhan Tasbolatov <snovitoll@gmail.com> wrote:
> >
> > 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() explicitly for the memory corruption instrumentation.
> >
> > 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.
>
> I assume you retested. Did you also test the bpf_probe_read_kernel()
> false positive no longer appears?
I've tested on:
- x86_64 with KMSAN
- x86_64 with KASAN
- arm64 with HW_TAGS -- still failing
- arm64 with SW_TAGS
Please see the testing result in the following link:
https://gist.github.com/novitoll/e2ccb2162340f7f8a63b63ee3e0f9994

I've also tested bpf_probe_read_kernel() in x86_64 KMSAN build,
it does trigger KMSAN, though I don't see explicitly copy_from_kernel*
in stack frame. AFAIU, it's checked prior to it in text_poke_copy().

Attached the PoC in the comment of the link above:

root@syzkaller:/tmp# uname -a
Linux syzkaller 6.12.0-rc2-g441b500abd70 #10 SMP PREEMPT_DYNAMIC Wed
Oct 9 00:17:59 +05 2024 x86_64 GNU/Linux
root@syzkaller:/tmp# ./exploit
[*] exploit start
[+] program loaded!
[ 139.778255] =====================================================
[ 139.778846] BUG: KMSAN: uninit-value in bcmp+0x155/0x290
[ 139.779311] bcmp+0x155/0x290
[ 139.779591] __text_poke+0xe2d/0x1120
[ 139.779950] text_poke_copy+0x1e7/0x2b0
[ 139.780297] bpf_arch_text_copy+0x41/0xa0
[ 139.780665] bpf_dispatcher_change_prog+0x12dd/0x16b0
[ 139.781324] bpf_prog_test_run_xdp+0xbf0/0x1d20
[ 139.781898] bpf_prog_test_run+0x5d6/0x9a0
[ 139.782372] __sys_bpf+0x758/0xf10
[ 139.782759] __x64_sys_bpf+0xdd/0x130
[ 139.783178] x64_sys_call+0x1a21/0x4e10
[ 139.783610] do_syscall_64+0xcd/0x1b0
[ 139.784039] entry_SYSCALL_64_after_hwframe+0x67/0x6f
[ 139.784597]
[ 139.784779] Uninit was created at:
[ 139.785197] __alloc_pages_noprof+0x717/0xe70
[ 139.785689] alloc_pages_bulk_noprof+0x17e1/0x20e0
[ 139.786223] alloc_pages_bulk_array_mempolicy_noprof+0x49e/0x5b0
[ 139.786873] __vmalloc_node_range_noprof+0xef2/0x24f0
[ 139.787414] execmem_alloc+0x1ec/0x4c0
[ 139.787841] bpf_jit_alloc_exec+0x3e/0x40
[ 139.788299] bpf_dispatcher_change_prog+0x430/0x16b0
[ 139.788837] bpf_prog_test_run_xdp+0xbf0/0x1d20
[ 139.789324] bpf_prog_test_run+0x5d6/0x9a0
[ 139.789774] __sys_bpf+0x758/0xf10
[ 139.790167] __x64_sys_bpf+0xdd/0x130
[ 139.790580] x64_sys_call+0x1a21/0x4e10
[ 139.791007] do_syscall_64+0xcd/0x1b0
[ 139.791423] entry_SYSCALL_64_after_hwframe+0x67/0x6f
>
> > Link: https://lore.kernel.org/linux-mm/CANpmjNMAVFzqnCZhEity9cjiqQ9CVN1X7qeeeAp_6yKjwKo8iw@mail.gmail.com/
> > Suggested-by: Marco Elver <elver@google.com>
>
> This looks more reasonable:
>
> Reviewed-by: Marco Elver <elver@google.com>
>
> This looks like the most conservative thing to do for now.
Done.
>
> > Reported-by: syzbot+61123a5daeb9f7454599@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=61123a5daeb9f7454599
> > Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
> > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> > ---
> > v2:
> > - squashed previous submitted in -mm tree 2 patches based on Linus tree
> > v3:
> > - moved checks to *_nofault_loop macros per Marco's comments
> > - edited the commit message
> > ---
> >  mm/kasan/kasan_test_c.c | 27 +++++++++++++++++++++++++++
> >  mm/kmsan/kmsan_test.c   | 17 +++++++++++++++++
> >  mm/maccess.c            | 10 ++++++++--
> >  3 files changed, 52 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
> > index a181e4780d9d..5cff90f831db 100644
> > --- a/mm/kasan/kasan_test_c.c
> > +++ b/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_test_cases[] = {
> >         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),
> >         {}
> >  };
> > diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
> > index 13236d579eba..9733a22c46c1 100644
> > --- a/mm/kmsan/kmsan_test.c
> > +++ b/mm/kmsan/kmsan_test.c
> > @@ -640,6 +640,22 @@ static void test_unpoison_memory(struct kunit *test)
> >         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_cases[] = {
> >         KUNIT_CASE(test_long_origin_chain),
> >         KUNIT_CASE(test_stackdepot_roundtrip),
> >         KUNIT_CASE(test_unpoison_memory),
> > +       KUNIT_CASE(test_copy_from_kernel_nofault),
> >         {},
> >  };
> >
> > diff --git a/mm/maccess.c b/mm/maccess.c
> > index 518a25667323..3ca55ec63a6a 100644
> > --- a/mm/maccess.c
> > +++ b/mm/maccess.c
> > @@ -13,9 +13,14 @@ bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
> >         return true;
> >  }
> >
> > +/*
> > + * The below only uses kmsan_check_memory() to ensure uninitialized kernel
> > + * memory isn't leaked.
> > + */
> >  #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);        \
> > +               kmsan_check_memory(src, sizeof(type));                  \
> >                 dst += sizeof(type);                                    \
> >                 src += sizeof(type);                                    \
> >                 len -= sizeof(type);                                    \
> > @@ -49,7 +54,8 @@ EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
> >
> >  #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);        \
> > +               instrument_write(dst, sizeof(type));                    \
> >                 dst += sizeof(type);                                    \
> >                 src += sizeof(type);                                    \
> >                 len -= sizeof(type);                                    \
> > --
> > 2.34.1
> >
diff mbox series

Patch

diff --git a/mm/kasan/kasan_test_c.c b/mm/kasan/kasan_test_c.c
index a181e4780d9d..5cff90f831db 100644
--- a/mm/kasan/kasan_test_c.c
+++ b/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_test_cases[] = {
 	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),
 	{}
 };
diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index 13236d579eba..9733a22c46c1 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -640,6 +640,22 @@  static void test_unpoison_memory(struct kunit *test)
 	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_cases[] = {
 	KUNIT_CASE(test_long_origin_chain),
 	KUNIT_CASE(test_stackdepot_roundtrip),
 	KUNIT_CASE(test_unpoison_memory),
+	KUNIT_CASE(test_copy_from_kernel_nofault),
 	{},
 };
 
diff --git a/mm/maccess.c b/mm/maccess.c
index 518a25667323..3ca55ec63a6a 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -13,9 +13,14 @@  bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
 	return true;
 }
 
+/*
+ * The below only uses kmsan_check_memory() to ensure uninitialized kernel
+ * memory isn't leaked.
+ */
 #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);	\
+		kmsan_check_memory(src, sizeof(type));			\
 		dst += sizeof(type);					\
 		src += sizeof(type);					\
 		len -= sizeof(type);					\
@@ -49,7 +54,8 @@  EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
 
 #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);	\
+		instrument_write(dst, sizeof(type));			\
 		dst += sizeof(type);					\
 		src += sizeof(type);					\
 		len -= sizeof(type);					\