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SubjectRe: [RFC PATCH 2/2] KUnit: KASAN Integration
On Thu, Feb 27, 2020 at 6:04 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> On Wed, 26 Feb 2020, Patricia Alfonso wrote:
>
> > Integrate KASAN into KUnit testing framework.
>
> This is a great idea! Some comments/suggestions below...
>

Thank you so much for your suggestions!

> > - Fail tests when KASAN reports an error that is not expected
> > - Use KUNIT_EXPECT_KASAN_FAIL to expect a KASAN error in KASAN tests
> > - KUnit struct added to current task to keep track of the current test
> > from KASAN code
> > - Booleans representing if a KASAN report is expected and if a KASAN
> > report is found added to kunit struct
> > - This prints "line# has passed" or "line# has failed"
> >
> > Signed-off-by: Patricia Alfonso <trishalfonso@google.com>
> > ---
> > If anyone has any suggestions on how best to print the failure
> > messages, please share!
> >
> > One issue I have found while testing this is the allocation fails in
> > kmalloc_pagealloc_oob_right() sometimes, but not consistently. This
> > does cause the test to fail on the KUnit side, as expected, but it
> > seems to skip all the tests before this one because the output starts
> > with this failure instead of with the first test, kmalloc_oob_right().
> >
> > include/kunit/test.h | 24 ++++++++++++++++++++++++
> > include/linux/sched.h | 7 ++++++-
> > lib/kunit/test.c | 7 ++++++-
> > mm/kasan/report.c | 19 +++++++++++++++++++
> > tools/testing/kunit/kunit_kernel.py | 2 +-
> > 5 files changed, 56 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/kunit/test.h b/include/kunit/test.h
> > index 2dfb550c6723..2e388f8937f3 100644
> > --- a/include/kunit/test.h
> > +++ b/include/kunit/test.h
> > @@ -21,6 +21,8 @@ struct kunit_resource;
> > typedef int (*kunit_resource_init_t)(struct kunit_resource *, void *);
> > typedef void (*kunit_resource_free_t)(struct kunit_resource *);
> >
> > +void kunit_set_failure(struct kunit *test);
> > +
> > /**
> > * struct kunit_resource - represents a *test managed resource*
> > * @allocation: for the user to store arbitrary data.
> > @@ -191,6 +193,9 @@ struct kunit {
> > * protect it with some type of lock.
> > */
> > struct list_head resources; /* Protected by lock. */
> > +
> > + bool kasan_report_expected;
> > + bool kasan_report_found;
> > };
> >
>
> Is this needed here? You're testing something pretty
> specific so it seems wrong to add to the generic
> kunit resource unless there's a good reason. I see the
> code around setting these values in mm/kasan/report.c,
> but I wonder if we could do something more generic.
>
> How about the concept of a static resource (assuming a
> dynamically allocated one is out because it messes
> with memory allocation tests)? Something like this:
>
> #define kunit_add_static_resource(test, resource_ptr, resource_field) \
> do { \
> spin_lock(&test->lock); \
> (resource_ptr)->resource_field.init = NULL; \
> (resource_ptr)->resource_field.free = NULL; \
> list_add_tail(&(resource_ptr)->resource_field, \
> &test->resources); \
> spin_unlock(&test->lock); \
> } while (0)
>
>
> Within your kasan code you could then create a kasan-specific
> structure that embends a kunit_resource, and contains the
> values you need:
>
> struct kasan_report_resource {
> struct kunit_resource res;
> bool kasan_report_expected;
> bool kasan_report_found;
> };
>
> (One thing we'd need to do for such static resources is fix
> kunit_resource_free() to check if there's a free() function,
> and if not assume a static resource)
>
> If you then create an init() function associated with your
> kunit suite (which will be run for every case) it can do this:
>
> int kunit_kasan_test_init(struct kunit *test)
> {
> kunit_add_static_resource(test, &my_kasan_report_resource, res);
> ...
> }
>
> The above should also be used to initialize current->kasan_unit_test
> instead of doing that in kunit_try_run_case(). With those
> changes, you don't (I think) need to change anything in core
> kunit (assuming support for static resources).
>
> To retrieve the resource during tests or in kasan context, the
> method seems to be to use kunit_resource_find(). However, that
> requires a match function which seems a bit heavyweight for the
> static case. We should probably have a default "find by name"
> or similar function here, and add an optional "name" field
> to kunit resources to simplify things. Anyway here you'd
> use something like:
>
> kasan_report_resource = kunit_resource_find(test, matchfn,
> NULL, matchdata);
>
>
> Are there any barriers to taking this sort of approach (apart
> from the support for static resources not being there yet)?
>

I'm not sure. I don't have any experience with kunit resources so I
would have to put some more effort into understanding how this would
work for myself. I wonder if this might be a bit of an over
complicated way of eliminating an extraneous boolean... maybe we can
find a simpler solution for the first version of this patch and add
the notion of a static resource for generic use later.

> > void kunit_init_test(struct kunit *test, const char *name);
> > @@ -941,6 +946,25 @@ do { \
> > ptr, \
> > NULL)
> >
> > +/**
> > + * KUNIT_EXPECT_KASAN_FAIL() - Causes a test failure when the expression does
> > + * not cause a KASAN error.
> > + *
> > + */
> > +#define KUNIT_EXPECT_KASAN_FAIL(test, condition) do { \
> > + test->kasan_report_expected = true; \
> > + test->kasan_report_found = false; \
> > + condition; \
> > + if (test->kasan_report_found == test->kasan_report_expected) { \
> > + pr_info("%d has passed", __LINE__); \
> > + } else { \
> > + kunit_set_failure(test); \
> > + pr_info("%d has failed", __LINE__); \
> > + } \
> > + test->kasan_report_expected = false; \
> > + test->kasan_report_found = false; \
> > +} while (0)
> > +
>
> Feels like this belongs in test_kasan.c, and could be reworked
> to avoid adding test->kasan_report_[expected|found] as described
> above.

You're right. Since I don't see any reason why any other tests should
want to expect a KASAN error, it does make sense to move this logic
inside test_kasan.c. If, in the future, there is a need for this
elsewhere, we can always move it back then.

> Instead of having your own pass/fail logic couldn't you
> do this:
>
> KUNIT_EXPECT_EQ(test, expected, found);
>
> ? That will set the failure state too so no need to export
> a separate function for that, and no need to log anything
> as KUNIT_EXPECT_EQ() should do that for you.
>

This is a great idea - I feel a little silly that I didn't think of
that myself! Do we think the failure message for the KUNIT_EXPECT_EQ()
would be sufficient for KASAN developers?
i.e. "Expected kasan_report_expected == kasan_report_found, but
kasan_report_expected == true
kasan_report_found == false"

> > /**
> > * KUNIT_EXPECT_TRUE() - Causes a test failure when the expression is not true.
> > * @test: The test context object.
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 04278493bf15..db23d56061e7 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -32,6 +32,8 @@
> > #include <linux/posix-timers.h>
> > #include <linux/rseq.h>
> >
> > +#include <kunit/test.h>
> > +
>
> This feels like the wrong place to add this #include, and
> when I attempted to build to test I ran into a bunch of
> compilation errors; for example:
>
> CC kernel/sched/core.o
> In file included from ./include/linux/uaccess.h:11,
> from ./arch/x86/include/asm/fpu/xstate.h:5,
> from ./arch/x86/include/asm/pgtable.h:26,
> from ./include/linux/kasan.h:16,
> from ./include/linux/slab.h:136,
> from ./include/kunit/test.h:16,
> from ./include/linux/sched.h:35,
> from init/do_mounts.c:3:
> ./arch/x86/include/asm/uaccess.h: In function 'set_fs':
> ./arch/x86/include/asm/uaccess.h:32:9: error: dereferencing pointer to
> incomplete type 'struct task_struct'
> current->thread.addr_limit = fs;
>
> (I'm testing with CONFIG_SLUB). Removing this #include
> resolves these errors, but then causes problems for
> lib/test_kasan.c. I'll dig around a bit more.
>

Yes, I was only testing with UML. Removing that #include fixed the
problem for me for both x86 and UML. Could you share more about the
errors you have encountered in lib/test_kasan.c?

> > /* task_struct member predeclarations (sorted alphabetically): */
> > struct audit_context;
> > struct backing_dev_info;
> > @@ -1178,7 +1180,10 @@ struct task_struct {
> >
> > #ifdef CONFIG_KASAN
> > unsigned int kasan_depth;
> > -#endif
> > +#ifdef CONFIG_KUNIT
> > + struct kunit *kasan_kunit_test;
> > +#endif /* CONFIG_KUNIT */
> > +#endif /* CONFIG_KASAN */
> >
> > #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> > /* Index of current stored address in ret_stack: */
> > diff --git a/lib/kunit/test.c b/lib/kunit/test.c
> > index 9242f932896c..d266b9495c67 100644
> > --- a/lib/kunit/test.c
> > +++ b/lib/kunit/test.c
> > @@ -9,11 +9,12 @@
> > #include <kunit/test.h>
> > #include <linux/kernel.h>
> > #include <linux/sched/debug.h>
> > +#include <linux/sched.h>
> >
> > #include "string-stream.h"
> > #include "try-catch-impl.h"
> >
> > -static void kunit_set_failure(struct kunit *test)
> > +void kunit_set_failure(struct kunit *test)
> > {
> > WRITE_ONCE(test->success, false);
> > }
> > @@ -236,6 +237,10 @@ static void kunit_try_run_case(void *data)
> > struct kunit_suite *suite = ctx->suite;
> > struct kunit_case *test_case = ctx->test_case;
> >
> > +#ifdef CONFIG_KASAN
> > + current->kasan_kunit_test = test;
> > +#endif
> > +
> > /*
> > * kunit_run_case_internal may encounter a fatal error; if it does,
> > * abort will be called, this thread will exit, and finally the parent
> > diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> > index 5ef9f24f566b..5554d23799a5 100644
> > --- a/mm/kasan/report.c
> > +++ b/mm/kasan/report.c
> > @@ -32,6 +32,8 @@
> >
> > #include <asm/sections.h>
> >
> > +#include <kunit/test.h>
> > +
> > #include "kasan.h"
> > #include "../slab.h"
> >
> > @@ -461,6 +463,15 @@ void kasan_report_invalid_free(void *object, unsigned long ip)
> > u8 tag = get_tag(object);
> >
> > object = reset_tag(object);
> > +
> > + if (current->kasan_kunit_test) {
> > + if (current->kasan_kunit_test->kasan_report_expected) {
> > + current->kasan_kunit_test->kasan_report_found = true;
> > + return;
> > + }
> > + kunit_set_failure(current->kasan_kunit_test);
> > + }
> > +
> > start_report(&flags);
> > pr_err("BUG: KASAN: double-free or invalid-free in %pS\n", (void *)ip);
> > print_tags(tag, object);
> > @@ -481,6 +492,14 @@ void __kasan_report(unsigned long addr, size_t size, bool is_write, unsigned lon
> > if (likely(!report_enabled()))
> > return;
> >
> > + if (current->kasan_kunit_test) {
> > + if (current->kasan_kunit_test->kasan_report_expected) {
> > + current->kasan_kunit_test->kasan_report_found = true;
> > + return;
> > + }
> > + kunit_set_failure(current->kasan_kunit_test);
> > + }
> > +
> > disable_trace_on_warning();
> >
> > tagged_addr = (void *)addr;
> > diff --git a/tools/testing/kunit/kunit_kernel.py b/tools/testing/kunit/kunit_kernel.py
> > index cc5d844ecca1..63eab18a8c34 100644
> > --- a/tools/testing/kunit/kunit_kernel.py
> > +++ b/tools/testing/kunit/kunit_kernel.py
> > @@ -141,7 +141,7 @@ class LinuxSourceTree(object):
> > return True
> >
> > def run_kernel(self, args=[], timeout=None, build_dir=''):
> > - args.extend(['mem=256M'])
> > + args.extend(['mem=256M', 'kasan_multi_shot'])
> > process = self._ops.linux_bin(args, timeout, build_dir)
> > with open(os.path.join(build_dir, 'test.log'), 'w') as f:
> > for line in process.stdout:
>
> I tried applying this to the "kunit" branch of linux-kselftest, and
> the above failed. Which branch are you building with? Probably
> best to use the kunit branch I think. Thanks!
>
I believe I am on Torvalds/master. There was some debate as to which
branch I should be developing on when I started, but it probably makes
sense for me to move to the "kunit" branch.

> Alan
>
> > --
> > 2.25.0.265.gbab2e86ba0-goog
> >
> >

--
Thank you for all your comments!
Patricia Alfonso

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