From a5e090acbf545c0a3b04080f8a488b17ec41fe02 Mon Sep 17 00:00:00 2001 From: Russell King Date: Wed, 19 Aug 2015 20:40:41 +0100 Subject: ARM: software-based priviledged-no-access support Provide a software-based implementation of the priviledged no access support found in ARMv8.1. Userspace pages are mapped using a different domain number from the kernel and IO mappings. If we switch the user domain to "no access" when we enter the kernel, we can prevent the kernel from touching userspace. However, the kernel needs to be able to access userspace via the various user accessor functions. With the wrapping in the previous patch, we can temporarily enable access when the kernel needs user access, and re-disable it afterwards. This allows us to trap non-intended accesses to userspace, eg, caused by an inadvertent dereference of the LIST_POISON* values, which, with appropriate user mappings setup, can be made to succeed. This in turn can allow use-after-free bugs to be further exploited than would otherwise be possible. Signed-off-by: Russell King --- arch/arm/include/asm/assembler.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) (limited to 'arch/arm/include/asm/assembler.h') diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h index a91177043467..3ae0eda5e64f 100644 --- a/arch/arm/include/asm/assembler.h +++ b/arch/arm/include/asm/assembler.h @@ -446,15 +446,45 @@ THUMB( orr \reg , \reg , #PSR_T_BIT ) .endm .macro uaccess_disable, tmp, isb=1 +#ifdef CONFIG_CPU_SW_DOMAIN_PAN + /* + * Whenever we re-enter userspace, the domains should always be + * set appropriately. + */ + mov \tmp, #DACR_UACCESS_DISABLE + mcr p15, 0, \tmp, c3, c0, 0 @ Set domain register + .if \isb + instr_sync + .endif +#endif .endm .macro uaccess_enable, tmp, isb=1 +#ifdef CONFIG_CPU_SW_DOMAIN_PAN + /* + * Whenever we re-enter userspace, the domains should always be + * set appropriately. + */ + mov \tmp, #DACR_UACCESS_ENABLE + mcr p15, 0, \tmp, c3, c0, 0 + .if \isb + instr_sync + .endif +#endif .endm .macro uaccess_save, tmp +#ifdef CONFIG_CPU_SW_DOMAIN_PAN + mrc p15, 0, \tmp, c3, c0, 0 + str \tmp, [sp, #S_FRAME_SIZE] +#endif .endm .macro uaccess_restore +#ifdef CONFIG_CPU_SW_DOMAIN_PAN + ldr r0, [sp, #S_FRAME_SIZE] + mcr p15, 0, r0, c3, c0, 0 +#endif .endm .macro uaccess_save_and_disable, tmp -- cgit v1.2.3