| From e265bbe87708508fccab82e82d2b6dffddd34021 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Wed, 30 Jun 2021 18:56:59 -0700 |
| Subject: selftests/vm/pkeys: refill shadow register after implicit kernel |
| write |
| |
| 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 */ |
| -- |
| 2.30.2 |
| |