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x86/pkeys: Add check for pkey "overflow"

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[ Upstream commit 16171bffc829272d5e6014bad48f680cb50943d9 ]

Alex Shi reported the pkey macros above arch_set_user_pkey_access()
to be unused.  They are unused, and even refer to a nonexistent
CONFIG option.

But, they might have served a good use, which was to ensure that
the code does not try to set values that would not fit in the
PKRU register.  As it stands, a too-large 'pkey' value would
be likely to silently overflow the u32 new_pkru_bits.

Add a check to look for overflows.  Also add a comment to remind
any future developer to closely examine the types used to store
pkey values if arch_max_pkey() ever changes.

This boots and passes the x86 pkey selftests.

Reported-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Dave Hansen <dave.hansen@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200122165346.AD4DA150@viggo.jf.intel.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Dave Hansen 2020-01-22 08:53:46 -08:00 committed by Greg Kroah-Hartman
parent eec0eacf6c
commit 03dda95667
2 changed files with 12 additions and 2 deletions
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5
arch/x86/include/asm/pkeys.h
View file

@ -4,6 +4,11 @@
#define ARCH_DEFAULT_PKEY 0
/*
* If more than 16 keys are ever supported, a thorough audit
* will be necessary to ensure that the types that store key
* numbers and masks have sufficient capacity.
*/
#define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1)
extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,

9
arch/x86/kernel/fpu/xstate.c
View file

@ -907,8 +907,6 @@ const void *get_xsave_field_ptr(int xsave_state)
#ifdef CONFIG_ARCH_HAS_PKEYS
#define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2)
#define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1)
/*
* This will go out and modify PKRU register to set the access
* rights for @pkey to @init_val.
@ -927,6 +925,13 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
if (!boot_cpu_has(X86_FEATURE_OSPKE))
return -EINVAL;
/*
* This code should only be called with valid 'pkey'
* values originating from in-kernel users. Complain
* if a bad value is observed.
*/
WARN_ON_ONCE(pkey >= arch_max_pkey());
/* Set the bits we need in PKRU: */
if (init_val & PKEY_DISABLE_ACCESS)
new_pkru_bits |= PKRU_AD_BIT;