linux-kernel - [PATCH 5.13 777/800] selftests/vm/pkeys: refill shadow register after implicit kernel write

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Date:   Mon, 12 Jul 2021 08:13:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>,
        Sandipan Das <sandipan@...ux.ibm.com>,
        Florian Weimer <fweimer@...hat.com>,
        "Desnes A. Nunes do Rosario" <desnesn@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...nel.org>,
        Michal Suchanek <msuchanek@...e.de>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.13 777/800] selftests/vm/pkeys: refill shadow register after implicit kernel write

From: Dave Hansen <dave.hansen@...ux.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@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Cc: Ram Pai <linuxram@...ibm.com>
Cc: Sandipan Das <sandipan@...ux.ibm.com>
Cc: Florian Weimer <fweimer@...hat.com>
Cc: "Desnes A. Nunes do Rosario" <desnesn@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Michal Suchanek <msuchanek@...e.de>
Cc: Shuah Khan <shuah@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.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