This is a note to let you know that I've just added the patch titled
selftests/vm/pkeys: fix alloc_random_pkey() to make it really, really random
to the 5.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
selftests-vm-pkeys-fix-alloc_random_pkey-to-make-it-.patch
and it can be found in the queue-5.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit b60ac855fa2b5735c8e809e8424039949bdd2604
Author: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Date: Wed Jun 30 18:56:53 2021 -0700
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@xxxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20210611164155.192D00FF@xxxxxxxxxxxxxxxxxx
Fixes: 6e373263ce07 ("selftests/vm/pkeys: fix alloc_random_pkey() to make it really random")
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Ram Pai <linuxram@xxxxxxxxxx>
Cc: Sandipan Das <sandipan@xxxxxxxxxxxxx>
Cc: Florian Weimer <fweimer@xxxxxxxxxx>
Cc: "Desnes A. Nunes do Rosario" <desnesn@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Suchanek <msuchanek@xxxxxxx>
Cc: Shuah Khan <shuah@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c
index fdbb602ecf32..9ee0ae5d3e06 100644
--- a/tools/testing/selftests/vm/protection_keys.c
+++ b/tools/testing/selftests/vm/protection_keys.c
@@ -561,7 +561,6 @@ 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;
@@ -1552,6 +1551,8 @@ int main(void)
int nr_iterations = 22;
int pkeys_supported = is_pkeys_supported();
+ srand((unsigned int)time(NULL));
+
setup_handlers();
printf("has pkeys: %d\n", pkeys_supported);
