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| author | Dave Hansen <dave.hansen@linux.intel.com> | 2021-07-01 04:56:53 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-20 17:17:41 +0300 |
| commit | c59680b9281e1f7f7717cd071a4df3b1c553214a (patch) | |
| tree | 15a14a2b6bef8afb30a330cf47a3eb5f6007e926 | |
| parent | 6f10741b1366bafc510297fe18bd08344d768ecb (diff) | |
| download | linux-c59680b9281e1f7f7717cd071a4df3b1c553214a.tar.xz | |
selftests/vm/pkeys: fix alloc_random_pkey() to make it really, really random
[ Upstream commit f36ef407628835a7d7fb3d235b1f1aac7022d9a3 ]
Patch series "selftests/vm/pkeys: Bug fixes and a new test".
There has been a lot of activity on the x86 front around the XSAVE
architecture which is used to context-switch processor state (among other
things). In addition, AMD has recently joined the protection keys club by
adding processor support for PKU.
The AMD implementation helped uncover a kernel bug around the PKRU "init
state", which actually applied to Intel's implementation but was just
harder to hit. This series adds a test which is expected to help find
this class of bug both on AMD and Intel. All the work around pkeys on x86
also uncovered a few bugs in the selftest.
This patch (of 4):
The "random" pkey allocation code currently does the good old:
srand((unsigned int)time(NULL));
*But*, it unfortunately does this on every random pkey allocation.
There may be thousands of these a second. time() has a one second
resolution. So, each time alloc_random_pkey() is called, the PRNG is
*RESET* to time(). This is nasty. Normally, if you do:
srand(<ANYTHING>);
foo = rand();
bar = rand();
You'll be quite guaranteed that 'foo' and 'bar' are different. But, if
you do:
srand(1);
foo = rand();
srand(1);
bar = rand();
You are quite guaranteed that 'foo' and 'bar' are the *SAME*. The recent
"fix" effectively forced the test case to use the same "random" pkey for
the whole test, unless the test run crossed a second boundary.
Only run srand() once at program startup.
This explains some very odd and persistent test failures I've been seeing.
Link: https://lkml.kernel.org/r/20210611164153.91B76FB8@viggo.jf.intel.com
Link: https://lkml.kernel.org/r/20210611164155.192D00FF@viggo.jf.intel.com
Fixes: 6e373263ce07 ("selftests/vm/pkeys: fix alloc_random_pkey() to make it really random")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ram Pai <linuxram@us.ibm.com>
Cc: Sandipan Das <sandipan@linux.ibm.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: "Desnes A. Nunes do Rosario" <desnesn@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Suchanek <msuchanek@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | tools/testing/selftests/x86/protection_keys.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/tools/testing/selftests/x86/protection_keys.c b/tools/testing/selftests/x86/protection_keys.c index b8778960da10..27661302a698 100644 --- a/tools/testing/selftests/x86/protection_keys.c +++ b/tools/testing/selftests/x86/protection_keys.c @@ -613,7 +613,6 @@ int alloc_random_pkey(void) int nr_alloced = 0; int random_index; memset(alloced_pkeys, 0, sizeof(alloced_pkeys)); - srand((unsigned int)time(NULL)); /* allocate every possible key and make a note of which ones we got */ max_nr_pkey_allocs = NR_PKEYS; @@ -1479,6 +1478,8 @@ int main(void) { int nr_iterations = 22; + srand((unsigned int)time(NULL)); + setup_handlers(); printf("has pku: %d\n", cpu_has_pku()); |