The patch titled
Subject: selftests/vm/pkeys: refill shadow register after implicit kernel write
has been added to the -mm tree. Its filename is
selftests-vm-pkeys-refill-shadow-register-after-implicit-kernel-write.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/selftests-vm-pkeys-refill-shadow-register-after-implicit-kernel-write.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/selftests-vm-pkeys-refill-shadow-register-after-implicit-kernel-write.patch
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------------------------------------------------------
From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Subject: selftests/vm/pkeys: refill shadow register after implicit kernel write
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@xxxxxxxxxxxxxxxxxx
Fixes: 6af17cf89e99 ("x86/pkeys/selftests: Add PROT_EXEC test")
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@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: "Aneesh Kumar K.V" <aneesh.kumar@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>
---
tools/testing/selftests/vm/protection_keys.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/tools/testing/selftests/vm/protection_keys.c~selftests-vm-pkeys-refill-shadow-register-after-implicit-kernel-write
+++ a/tools/testing/selftests/vm/protection_keys.c
@@ -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 */
_
Patches currently in -mm which might be from dave.hansen@xxxxxxxxxxxxxxx are
selftests-vm-pkeys-fix-alloc_random_pkey-to-make-it-really-really-random.patch
selftests-vm-pkeys-handle-negative-sys_pkey_alloc-return-code.patch
selftests-vm-pkeys-refill-shadow-register-after-implicit-kernel-write.patch
selftests-vm-pkeys-exercise-x86-xsave-init-state.patch
