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Commit 03dda956 authored by Dave Hansen's avatar Dave Hansen Committed by Greg Kroah-Hartman
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x86/pkeys: Add check for pkey "overflow" 



[ 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: default avatarAlex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@intel.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200122165346.AD4DA150@viggo.jf.intel.com


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent eec0eacf

arch/x86/include/asm/pkeys.h

+5 −0
Original line number Diff line number Diff line
@@ -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,

arch/x86/kernel/fpu/xstate.c

+7 −2
Original line number Diff line number Diff line
@@ -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;