Messages in this thread Patch in this message | | | Subject | [PATCH 3/4] selftests/vm/pkeys: Refill shadow register after implicit kernel write | From | Dave Hansen <> | Date | Fri, 11 Jun 2021 09:42:00 -0700 |
| |
From: Dave Hansen <dave.hansen@linux.intel.com>
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().
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> Cc: Ram Pai <linuxram@us.ibm.com> Cc: Sandipan Das <sandipan@linux.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> 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: "Aneesh Kumar K.V" <aneesh.kumar@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> Cc: x86@kernel.org ---
b/tools/testing/selftests/vm/protection_keys.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff -puN tools/testing/selftests/vm/protection_keys.c~selftests_vm_pkeys_Refill_shadow_register_after_implict_kernel_write-1 tools/testing/selftests/vm/protection_keys.c --- a/tools/testing/selftests/vm/protection_keys.c~selftests_vm_pkeys_Refill_shadow_register_after_implict_kernel_write-1 2021-06-11 09:41:33.508468061 -0700 +++ b/tools/testing/selftests/vm/protection_keys.c 2021-06-11 09:41:33.517468061 -0700 @@ -1448,6 +1448,13 @@ void test_implicit_mprotect_exec_only_me 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 */ _
| |