x86/pkeys: Add check for pkey "overflow"
[ Upstream commit 16171bffc8
]
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>
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@ -4,6 +4,11 @@
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#define ARCH_DEFAULT_PKEY 0
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/*
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* If more than 16 keys are ever supported, a thorough audit
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* will be necessary to ensure that the types that store key
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* numbers and masks have sufficient capacity.
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*/
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#define arch_max_pkey() (boot_cpu_has(X86_FEATURE_OSPKE) ? 16 : 1)
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extern int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
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@ -895,8 +895,6 @@ const void *get_xsave_field_ptr(int xfeature_nr)
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#ifdef CONFIG_ARCH_HAS_PKEYS
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#define NR_VALID_PKRU_BITS (CONFIG_NR_PROTECTION_KEYS * 2)
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#define PKRU_VALID_MASK (NR_VALID_PKRU_BITS - 1)
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/*
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* This will go out and modify PKRU register to set the access
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* rights for @pkey to @init_val.
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@ -915,6 +913,13 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
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if (!boot_cpu_has(X86_FEATURE_OSPKE))
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return -EINVAL;
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/*
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* This code should only be called with valid 'pkey'
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* values originating from in-kernel users. Complain
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* if a bad value is observed.
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*/
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WARN_ON_ONCE(pkey >= arch_max_pkey());
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/* Set the bits we need in PKRU: */
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if (init_val & PKEY_DISABLE_ACCESS)
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new_pkru_bits |= PKRU_AD_BIT;
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