[PATCH bpf v1 0/3] Test the 32bit narrow reads

[PATCH bpf v1 0/3] Test the 32bit narrow reads

[Krzesimir Nowak]

These patches try to test the fix made in commit e2f7fc0ac695 ("bpf:
fix undefined behavior in narrow load handling"). The problem existed
in the generated BPF bytecode that was doing a 32bit narrow read of a
64bit field, so to test it the code would need to be executed.
Currently the only such field exists in BPF_PROG_TYPE_PERF_EVENT,
which is not supported by bpf_prog_test_run().

First commit adds the test, but since I can't run it, I'm not sure if
it is even valid (because endianness, for example). Second commit adds
a message to test_verifier when it couldn't run the program because of
lack permissions or program type being not supported. Third commit
fixes a possible problem with errno.

With these patches, I get the following output on my test:

/kernel/tools/testing/selftests/bpf$ sudo ./test_verifier 920 920
#920/p 32bit loads of a 64bit field (both least and most significant words) Did not run the program (not supported) OK
Summary: 1 PASSED, 0 SKIPPED, 0 FAILED

So it looks like I need to pick a different approach.

Krzesimir Nowak (3):
  selftests/bpf: Test correctness of narrow 32bit read on 64bit field
  selftests/bpf: Print a message when tester could not run a program
  selftests/bpf: Avoid a clobbering of errno

 tools/testing/selftests/bpf/test_verifier.c   | 19 +++++++++++++++----
 .../testing/selftests/bpf/verifier/var_off.c  | 15 +++++++++++++++
 2 files changed, 30 insertions(+), 4 deletions(-)

-- 
2.20.1

[PATCH bpf v1 1/3] selftests/bpf: Test correctness of narrow 32bit read on 64bit field

[Krzesimir Nowak]

Test the correctness of the 32bit narrow reads by reading both halves
of the 64 bit field and doing a binary or on them to see if we get the
original value.

This isn't really tested - the program is not being run, because
BPF_PROG_TYPE_PERF_EVENT is not supported by bpf_test_run_prog.

Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
---
 tools/testing/selftests/bpf/verifier/var_off.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/tools/testing/selftests/bpf/verifier/var_off.c b/tools/testing/selftests/bpf/verifier/var_off.c
index 8504ac937809..2668819dcc85 100644
--- a/tools/testing/selftests/bpf/verifier/var_off.c
+++ b/tools/testing/selftests/bpf/verifier/var_off.c
@@ -246,3 +246,18 @@
 	.result = ACCEPT,
 	.prog_type = BPF_PROG_TYPE_LWT_IN,
 },
+{
+	"32bit loads of a 64bit field (both least and most significant words)",
+	.insns = {
+	BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
+	BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period) + 4),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
+	BPF_ALU64_IMM(BPF_LSH, BPF_REG_4, 32),
+	BPF_ALU64_REG(BPF_OR, BPF_REG_4, BPF_REG_5),
+	BPF_ALU64_REG(BPF_XOR, BPF_REG_4, BPF_REG_6),
+	BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT,
+	.prog_type = BPF_PROG_TYPE_PERF_EVENT,
+},
-- 
2.20.1

[PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Krzesimir Nowak]

This prints a message when the error is about program type being not
supported by the test runner or because of permissions problem. This
is to see if the program we expected to run was actually executed.

The messages are open-coded because strerror(ENOTSUPP) returns
"Unknown error 524".

Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
---
 tools/testing/selftests/bpf/test_verifier.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index ccd896b98cac..bf0da03f593b 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
 				tmp, &size_tmp, &retval, NULL);
 	if (unpriv)
 		set_admin(false);
-	if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
-		printf("Unexpected bpf_prog_test_run error ");
-		return err;
+	if (err) {
+		switch (errno) {
+		case 524/*ENOTSUPP*/:
+			printf("Did not run the program (not supported) ");
+			return 0;
+		case EPERM:
+			printf("Did not run the program (no permission) ");
+			return 0;
+		default:
+			printf("Unexpected bpf_prog_test_run error ");
+			return err;
+		}
 	}
-	if (!err && retval != expected_val &&
+	if (retval != expected_val &&
 	    expected_val != POINTER_VALUE) {
 		printf("FAIL retval %d != %d ", retval, expected_val);
 		return 1;
-- 
2.20.1

[PATCH bpf v1 3/3] selftests/bpf: Avoid a clobbering of errno

[Krzesimir Nowak]

Save errno right after bpf_prog_test_run returns, so we later check
the error code actually set by bpf_prog_test_run, not by some libcap
function.

Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
Fixes: 5a8d5209ac022 ("selftests: bpf: add trivial JSET tests")
Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
---
 tools/testing/selftests/bpf/test_verifier.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index bf0da03f593b..514e17246396 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -818,15 +818,17 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
 	__u32 size_tmp = sizeof(tmp);
 	uint32_t retval;
 	int err;
+	int saved_errno;
 
 	if (unpriv)
 		set_admin(true);
 	err = bpf_prog_test_run(fd_prog, 1, data, size_data,
 				tmp, &size_tmp, &retval, NULL);
+	saved_errno = errno;
 	if (unpriv)
 		set_admin(false);
 	if (err) {
-		switch (errno) {
+		switch (saved_errno) {
 		case 524/*ENOTSUPP*/:
 			printf("Did not run the program (not supported) ");
 			return 0;
-- 
2.20.1

Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Jakub Kicinski]

On Wed, 15 May 2019 15:47:27 +0200, Krzesimir Nowak wrote:
> This prints a message when the error is about program type being not
> supported by the test runner or because of permissions problem. This
> is to see if the program we expected to run was actually executed.
> 
> The messages are open-coded because strerror(ENOTSUPP) returns
> "Unknown error 524".
> 
> Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> ---
>  tools/testing/selftests/bpf/test_verifier.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index ccd896b98cac..bf0da03f593b 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
>  				tmp, &size_tmp, &retval, NULL);
>  	if (unpriv)
>  		set_admin(false);
> -	if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> -		printf("Unexpected bpf_prog_test_run error ");
> -		return err;
> +	if (err) {
> +		switch (errno) {
> +		case 524/*ENOTSUPP*/:
> +			printf("Did not run the program (not supported) ");
> +			return 0;
> +		case EPERM:
> +			printf("Did not run the program (no permission) ");
> +			return 0;

Perhaps use strerror(errno)?

> +		default:
> +			printf("Unexpected bpf_prog_test_run error ");
> +			return err;
> +		}
>  	}
> -	if (!err && retval != expected_val &&
> +	if (retval != expected_val &&
>  	    expected_val != POINTER_VALUE) {
>  		printf("FAIL retval %d != %d ", retval, expected_val);
>  		return 1;

Re: [PATCH bpf v1 3/3] selftests/bpf: Avoid a clobbering of errno

[Jakub Kicinski]

On Wed, 15 May 2019 15:47:28 +0200, Krzesimir Nowak wrote:
> Save errno right after bpf_prog_test_run returns, so we later check
> the error code actually set by bpf_prog_test_run, not by some libcap
> function.
> 
> Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
> Fixes: 5a8d5209ac022 ("selftests: bpf: add trivial JSET tests")

This commit (of mine) just moved this code into a helper, the bug is
older:

Fixes: 832c6f2c29ec ("bpf: test make sure to run unpriv test cases in test_verifier")

> Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> ---
>  tools/testing/selftests/bpf/test_verifier.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index bf0da03f593b..514e17246396 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -818,15 +818,17 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
>  	__u32 size_tmp = sizeof(tmp);
>  	uint32_t retval;
>  	int err;
> +	int saved_errno;
>  
>  	if (unpriv)
>  		set_admin(true);
>  	err = bpf_prog_test_run(fd_prog, 1, data, size_data,
>  				tmp, &size_tmp, &retval, NULL);
> +	saved_errno = errno;
>  	if (unpriv)
>  		set_admin(false);
>  	if (err) {
> -		switch (errno) {
> +		switch (saved_errno) {
>  		case 524/*ENOTSUPP*/:
>  			printf("Did not run the program (not supported) ");
>  			return 0;

Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Krzesimir Nowak]

On Wed, May 15, 2019 at 11:46 PM Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Wed, 15 May 2019 15:47:27 +0200, Krzesimir Nowak wrote:
> > This prints a message when the error is about program type being not
> > supported by the test runner or because of permissions problem. This
> > is to see if the program we expected to run was actually executed.
> >
> > The messages are open-coded because strerror(ENOTSUPP) returns
> > "Unknown error 524".
> >
> > Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> > ---
> >  tools/testing/selftests/bpf/test_verifier.c | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > index ccd896b98cac..bf0da03f593b 100644
> > --- a/tools/testing/selftests/bpf/test_verifier.c
> > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> >                               tmp, &size_tmp, &retval, NULL);
> >       if (unpriv)
> >               set_admin(false);
> > -     if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> > -             printf("Unexpected bpf_prog_test_run error ");
> > -             return err;
> > +     if (err) {
> > +             switch (errno) {
> > +             case 524/*ENOTSUPP*/:
> > +                     printf("Did not run the program (not supported) ");
> > +                     return 0;
> > +             case EPERM:
> > +                     printf("Did not run the program (no permission) ");
> > +                     return 0;
>
> Perhaps use strerror(errno)?

As I said in the commit message, I open-coded those messages because
strerror for ENOTSUPP returns "Unknown error 524".

>
> > +             default:
> > +                     printf("Unexpected bpf_prog_test_run error ");
> > +                     return err;
> > +             }
> >       }
> > -     if (!err && retval != expected_val &&
> > +     if (retval != expected_val &&
> >           expected_val != POINTER_VALUE) {
> >               printf("FAIL retval %d != %d ", retval, expected_val);
> >               return 1;
>


-- 
Kinvolk GmbH | Adalbertstr.6a, 10999 Berlin | tel: +491755589364
Geschäftsführer/Directors: Alban Crequy, Chris Kühl, Iago López Galeiras
Registergericht/Court of registration: Amtsgericht Charlottenburg
Registernummer/Registration number: HRB 171414 B
Ust-ID-Nummer/VAT ID number: DE302207000

Re: [PATCH bpf v1 3/3] selftests/bpf: Avoid a clobbering of errno

[Krzesimir Nowak]

On Wed, May 15, 2019 at 11:51 PM Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Wed, 15 May 2019 15:47:28 +0200, Krzesimir Nowak wrote:
> > Save errno right after bpf_prog_test_run returns, so we later check
> > the error code actually set by bpf_prog_test_run, not by some libcap
> > function.
> >
> > Cc: Jakub Kicinski <jakub.kicinski@netronome.com>
> > Fixes: 5a8d5209ac022 ("selftests: bpf: add trivial JSET tests")
>
> This commit (of mine) just moved this code into a helper, the bug is
> older:
>
> Fixes: 832c6f2c29ec ("bpf: test make sure to run unpriv test cases in test_verifier")

Oops, ok. Will fix it. Thanks.

>
> > Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> > ---
> >  tools/testing/selftests/bpf/test_verifier.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > index bf0da03f593b..514e17246396 100644
> > --- a/tools/testing/selftests/bpf/test_verifier.c
> > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > @@ -818,15 +818,17 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> >       __u32 size_tmp = sizeof(tmp);
> >       uint32_t retval;
> >       int err;
> > +     int saved_errno;
> >
> >       if (unpriv)
> >               set_admin(true);
> >       err = bpf_prog_test_run(fd_prog, 1, data, size_data,
> >                               tmp, &size_tmp, &retval, NULL);
> > +     saved_errno = errno;
> >       if (unpriv)
> >               set_admin(false);
> >       if (err) {
> > -             switch (errno) {
> > +             switch (saved_errno) {
> >               case 524/*ENOTSUPP*/:
> >                       printf("Did not run the program (not supported) ");
> >                       return 0;
>


-- 
Kinvolk GmbH | Adalbertstr.6a, 10999 Berlin | tel: +491755589364
Geschäftsführer/Directors: Alban Crequy, Chris Kühl, Iago López Galeiras
Registergericht/Court of registration: Amtsgericht Charlottenburg
Registernummer/Registration number: HRB 171414 B
Ust-ID-Nummer/VAT ID number: DE302207000

Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Jakub Kicinski]

On Thu, 16 May 2019 11:29:39 +0200, Krzesimir Nowak wrote:
> > > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > > index ccd896b98cac..bf0da03f593b 100644
> > > --- a/tools/testing/selftests/bpf/test_verifier.c
> > > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > > @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> > >                               tmp, &size_tmp, &retval, NULL);
> > >       if (unpriv)
> > >               set_admin(false);
> > > -     if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> > > -             printf("Unexpected bpf_prog_test_run error ");
> > > -             return err;
> > > +     if (err) {
> > > +             switch (errno) {
> > > +             case 524/*ENOTSUPP*/:
> > > +                     printf("Did not run the program (not supported) ");
> > > +                     return 0;
> > > +             case EPERM:
> > > +                     printf("Did not run the program (no permission) ");
> > > +                     return 0;  
> >
> > Perhaps use strerror(errno)?  
> 
> As I said in the commit message, I open-coded those messages because
> strerror for ENOTSUPP returns "Unknown error 524".

Ah, sorry, missed that.  I wonder if that's something worth addressing
in libc, since the BPF subsystem uses ENOTSUPP a lot.

Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Krzesimir Nowak]

On Thu, May 16, 2019 at 5:51 PM Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Thu, 16 May 2019 11:29:39 +0200, Krzesimir Nowak wrote:
> > > > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > > > index ccd896b98cac..bf0da03f593b 100644
> > > > --- a/tools/testing/selftests/bpf/test_verifier.c
> > > > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > > > @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> > > >                               tmp, &size_tmp, &retval, NULL);
> > > >       if (unpriv)
> > > >               set_admin(false);
> > > > -     if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> > > > -             printf("Unexpected bpf_prog_test_run error ");
> > > > -             return err;
> > > > +     if (err) {
> > > > +             switch (errno) {
> > > > +             case 524/*ENOTSUPP*/:
> > > > +                     printf("Did not run the program (not supported) ");
> > > > +                     return 0;
> > > > +             case EPERM:
> > > > +                     printf("Did not run the program (no permission) ");
> > > > +                     return 0;
> > >
> > > Perhaps use strerror(errno)?
> >
> > As I said in the commit message, I open-coded those messages because
> > strerror for ENOTSUPP returns "Unknown error 524".
>
> Ah, sorry, missed that.  I wonder if that's something worth addressing
> in libc, since the BPF subsystem uses ENOTSUPP a lot.

The "not supported" errno situation seems to be a mess. There is an
ENOTSUP define in libc. ENOTSUP is usually defined to be EOPNOTSUPP
(taken from kernel), which in turn seems to have a different value
(95) than kernel's ENOTSUPP (524). Adding ENOTSUPP (with two Ps) to
libc would only add to the confusion. So it's kind of meh and I guess
people just moved on with workarounds.

-- 
Kinvolk GmbH | Adalbertstr.6a, 10999 Berlin | tel: +491755589364
Geschäftsführer/Directors: Alban Crequy, Chris Kühl, Iago López Galeiras
Registergericht/Court of registration: Amtsgericht Charlottenburg
Registernummer/Registration number: HRB 171414 B
Ust-ID-Nummer/VAT ID number: DE302207000

Re: [PATCH bpf v1 2/3] selftests/bpf: Print a message when tester could not run a program

[Jakub Kicinski]

On Thu, 16 May 2019 18:21:32 +0200, Krzesimir Nowak wrote:
> On Thu, May 16, 2019 at 5:51 PM Jakub Kicinski wrote:
> > On Thu, 16 May 2019 11:29:39 +0200, Krzesimir Nowak wrote:  
> > > > > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > > > > index ccd896b98cac..bf0da03f593b 100644
> > > > > --- a/tools/testing/selftests/bpf/test_verifier.c
> > > > > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > > > > @@ -825,11 +825,20 @@ static int do_prog_test_run(int fd_prog, bool unpriv, uint32_t expected_val,
> > > > >                               tmp, &size_tmp, &retval, NULL);
> > > > >       if (unpriv)
> > > > >               set_admin(false);
> > > > > -     if (err && errno != 524/*ENOTSUPP*/ && errno != EPERM) {
> > > > > -             printf("Unexpected bpf_prog_test_run error ");
> > > > > -             return err;
> > > > > +     if (err) {
> > > > > +             switch (errno) {
> > > > > +             case 524/*ENOTSUPP*/:
> > > > > +                     printf("Did not run the program (not supported) ");
> > > > > +                     return 0;
> > > > > +             case EPERM:
> > > > > +                     printf("Did not run the program (no permission) ");
> > > > > +                     return 0;  
> > > >
> > > > Perhaps use strerror(errno)?  
> > >
> > > As I said in the commit message, I open-coded those messages because
> > > strerror for ENOTSUPP returns "Unknown error 524".  
> >
> > Ah, sorry, missed that.  I wonder if that's something worth addressing
> > in libc, since the BPF subsystem uses ENOTSUPP a lot.  
> 
> The "not supported" errno situation seems to be a mess. There is an
> ENOTSUP define in libc. ENOTSUP is usually defined to be EOPNOTSUPP
> (taken from kernel), which in turn seems to have a different value
> (95) than kernel's ENOTSUPP (524). Adding ENOTSUPP (with two Ps) to
> libc would only add to the confusion. So it's kind of meh and I guess
> people just moved on with workarounds.

Yes, ENOTSUP is never used in the kernel, but it's a mess.

This commit a while ago said ENOTSUPP is from NFS:

commit 423b3aecf29085a52530d4f9167c56a84b081042
Author: Or Gerlitz <ogerlitz@mellanox.com>
Date:   Thu Feb 23 12:02:41 2017 +0200

    net/mlx4: Change ENOTSUPP to EOPNOTSUPP
    
    As ENOTSUPP is specific to NFS, change the return error value to
    EOPNOTSUPP in various places in the mlx4 driver.
    
    Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
    Suggested-by: Yotam Gigi <yotamg@mellanox.com>
    Reviewed-by: Matan Barak <matanb@mellanox.com>
    Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>

But it's spreading throughout the kernel like a wildfire, I counted 1364
in my tree :/  Some are in tools/, but still.  My understanding was that
system calls should never return values above 512, but I'm probably
wrong about that.

Given the popularity, and the fact its an ABI at this point, we
probably have no choice but to add it to libc, but to be clear IMO it's
not a blocker for your patches.

Re: [PATCH bpf v1 1/3] selftests/bpf: Test correctness of narrow 32bit read on 64bit field

[Daniel Borkmann]

On 05/15/2019 03:47 PM, Krzesimir Nowak wrote:
> Test the correctness of the 32bit narrow reads by reading both halves
> of the 64 bit field and doing a binary or on them to see if we get the
> original value.
> 
> This isn't really tested - the program is not being run, because
> BPF_PROG_TYPE_PERF_EVENT is not supported by bpf_test_run_prog.

One option could be to add actual support for BPF_PROG_TYPE_PERF_EVENT to
test_verifier where the program gets actually triggered, and the result
stored in a map value that the test case reads out for checking the result
against the expected one. Recently added something similar for LRU maps in
the test suite, that shouldn't be too complex.

Thanks,
Daniel

> Signed-off-by: Krzesimir Nowak <krzesimir@kinvolk.io>
> ---
>  tools/testing/selftests/bpf/verifier/var_off.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/verifier/var_off.c b/tools/testing/selftests/bpf/verifier/var_off.c
> index 8504ac937809..2668819dcc85 100644
> --- a/tools/testing/selftests/bpf/verifier/var_off.c
> +++ b/tools/testing/selftests/bpf/verifier/var_off.c
> @@ -246,3 +246,18 @@
>  	.result = ACCEPT,
>  	.prog_type = BPF_PROG_TYPE_LWT_IN,
>  },
> +{
> +	"32bit loads of a 64bit field (both least and most significant words)",
> +	.insns = {
> +	BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
> +	BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period) + 4),
> +	BPF_LDX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, offsetof(struct bpf_perf_event_data, sample_period)),
> +	BPF_ALU64_IMM(BPF_LSH, BPF_REG_4, 32),
> +	BPF_ALU64_REG(BPF_OR, BPF_REG_4, BPF_REG_5),
> +	BPF_ALU64_REG(BPF_XOR, BPF_REG_4, BPF_REG_6),
> +	BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
> +	BPF_EXIT_INSN(),
> +	},
> +	.result = ACCEPT,
> +	.prog_type = BPF_PROG_TYPE_PERF_EVENT,
> +},
>