From: Dave Hansen dave.hansen@linux.intel.com
[ Upstream commit 6039ca254979694c5362dfebadd105e286c397bb ]
The pkey test code keeps a "shadow" of the pkey register around. This ensures that any bugs which might write to the register can be caught more quickly.
Generally, userspace has a good idea when the kernel is going to write to the register. For instance, alloc_pkey() is passed a permission mask. The caller of alloc_pkey() can update the shadow based on the return value and the mask.
But, the kernel can also modify the pkey register in a more sneaky way. For mprotect(PROT_EXEC) mappings, the kernel will allocate a pkey and write the pkey register to create an execute-only mapping. The kernel never tells userspace what key it uses for this.
This can cause the test to fail with messages like:
protection_keys_64.2: pkey-helpers.h:132: _read_pkey_reg: Assertion `pkey_reg == shadow_pkey_reg' failed.
because the shadow was not updated with the new kernel-set value.
Forcibly update the shadow value immediately after an mprotect().
Link: https://lkml.kernel.org/r/20210611164200.EF76AB73@viggo.jf.intel.com Fixes: 6af17cf89e99 ("x86/pkeys/selftests: Add PROT_EXEC test") 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 --- tools/testing/selftests/vm/protection_keys.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c index 356d62fca27f..87eecd5ba577 100644 --- a/tools/testing/selftests/vm/protection_keys.c +++ b/tools/testing/selftests/vm/protection_keys.c @@ -1448,6 +1448,13 @@ void test_implicit_mprotect_exec_only_memory(int *ptr, u16 pkey) ret = mprotect(p1, PAGE_SIZE, PROT_EXEC); pkey_assert(!ret);
+ /* + * Reset the shadow, assuming that the above mprotect() + * correctly changed PKRU, but to an unknown value since + * the actual alllocated pkey is unknown. + */ + shadow_pkey_reg = __read_pkey_reg(); + dprintf2("pkey_reg: %016llx\n", read_pkey_reg());
/* Make sure this is an *instruction* fault */