Commit 27a921e7 authored by Will Deacon's avatar Will Deacon
Browse files

arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN 



With the ASID now installed in TTBR1, we can re-enable ARM64_SW_TTBR0_PAN
by ensuring that we switch to a reserved ASID of zero when disabling
user access and restore the active user ASID on the uaccess enable path.

Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Tested-by: default avatarShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 158d4958

arch/arm64/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -910,7 +910,6 @@ endif 


config ARM64_SW_TTBR0_PAN

	bool "Emulate Privileged Access Never using TTBR0_EL1 switching"

	depends on BROKEN       # Temporary while switch_mm is reworked

	help

	  Enabling this option prevents the kernel from accessing

	  user-space memory directly by pointing TTBR0_EL1 to a reserved

arch/arm64/include/asm/asm-uaccess.h

+17 −8
Original line number Diff line number Diff line
@@ -16,11 +16,20 @@ 
	add	\tmp1, \tmp1, #SWAPPER_DIR_SIZE	// reserved_ttbr0 at the end of swapper_pg_dir

	msr	ttbr0_el1, \tmp1		// set reserved TTBR0_EL1

	isb

	sub	\tmp1, \tmp1, #SWAPPER_DIR_SIZE

	bic	\tmp1, \tmp1, #(0xffff << 48)

	msr	ttbr1_el1, \tmp1		// set reserved ASID

	isb

	.endm



	.macro	__uaccess_ttbr0_enable, tmp1

	.macro	__uaccess_ttbr0_enable, tmp1, tmp2

	get_thread_info \tmp1

	ldr	\tmp1, [\tmp1, #TSK_TI_TTBR0]	// load saved TTBR0_EL1

	mrs	\tmp2, ttbr1_el1

	extr    \tmp2, \tmp2, \tmp1, #48

	ror     \tmp2, \tmp2, #16

	msr	ttbr1_el1, \tmp2		// set the active ASID

	isb

	msr	ttbr0_el1, \tmp1		// set the non-PAN TTBR0_EL1

	isb

	.endm
@@ -31,18 +40,18 @@ alternative_if_not ARM64_HAS_PAN 
alternative_else_nop_endif

	.endm



	.macro	uaccess_ttbr0_enable, tmp1, tmp2

	.macro	uaccess_ttbr0_enable, tmp1, tmp2, tmp3

alternative_if_not ARM64_HAS_PAN

	save_and_disable_irq \tmp2		// avoid preemption

	__uaccess_ttbr0_enable \tmp1

	restore_irq \tmp2

	save_and_disable_irq \tmp3		// avoid preemption

	__uaccess_ttbr0_enable \tmp1, \tmp2

	restore_irq \tmp3

alternative_else_nop_endif

	.endm

#else

	.macro	uaccess_ttbr0_disable, tmp1

	.endm



	.macro	uaccess_ttbr0_enable, tmp1, tmp2

	.macro	uaccess_ttbr0_enable, tmp1, tmp2, tmp3

	.endm

#endif
@@ -56,8 +65,8 @@ alternative_if ARM64_ALT_PAN_NOT_UAO 
alternative_else_nop_endif

	.endm



	.macro	uaccess_enable_not_uao, tmp1, tmp2

	uaccess_ttbr0_enable \tmp1, \tmp2

	.macro	uaccess_enable_not_uao, tmp1, tmp2, tmp3

	uaccess_ttbr0_enable \tmp1, \tmp2, \tmp3

alternative_if ARM64_ALT_PAN_NOT_UAO

	SET_PSTATE_PAN(0)

alternative_else_nop_endif

arch/arm64/include/asm/uaccess.h

+17 −4
Original line number Diff line number Diff line
@@ -107,15 +107,19 @@ static inline void __uaccess_ttbr0_disable(void) 
{

	unsigned long ttbr;



	ttbr = read_sysreg(ttbr1_el1);

	/* reserved_ttbr0 placed at the end of swapper_pg_dir */

	ttbr = read_sysreg(ttbr1_el1) + SWAPPER_DIR_SIZE;

	write_sysreg(ttbr, ttbr0_el1);

	write_sysreg(ttbr + SWAPPER_DIR_SIZE, ttbr0_el1);

	isb();

	/* Set reserved ASID */

	ttbr &= ~(0xffffUL << 48);

	write_sysreg(ttbr, ttbr1_el1);

	isb();

}



static inline void __uaccess_ttbr0_enable(void)

{

	unsigned long flags;

	unsigned long flags, ttbr0, ttbr1;



	/*

	 * Disable interrupts to avoid preemption between reading the 'ttbr0'
@@ -123,7 +127,16 @@ static inline void __uaccess_ttbr0_enable(void) 
	 * roll-over and an update of 'ttbr0'.

	 */

	local_irq_save(flags);

	write_sysreg(current_thread_info()->ttbr0, ttbr0_el1);

	ttbr0 = current_thread_info()->ttbr0;



	/* Restore active ASID */

	ttbr1 = read_sysreg(ttbr1_el1);

	ttbr1 |= ttbr0 & (0xffffUL << 48);

	write_sysreg(ttbr1, ttbr1_el1);

	isb();



	/* Restore user page table */

	write_sysreg(ttbr0, ttbr0_el1);

	isb();

	local_irq_restore(flags);

}

arch/arm64/kernel/entry.S

+2 −2
Original line number Diff line number Diff line
@@ -184,7 +184,7 @@ alternative_if ARM64_HAS_PAN 
alternative_else_nop_endif



	.if	\el != 0

	mrs	x21, ttbr0_el1

	mrs	x21, ttbr1_el1

	tst	x21, #0xffff << 48		// Check for the reserved ASID

	orr	x23, x23, #PSR_PAN_BIT		// Set the emulated PAN in the saved SPSR

	b.eq	1f				// TTBR0 access already disabled
@@ -248,7 +248,7 @@ alternative_else_nop_endif 
	tbnz	x22, #22, 1f			// Skip re-enabling TTBR0 access if the PSR_PAN_BIT is set

	.endif



	__uaccess_ttbr0_enable x0

	__uaccess_ttbr0_enable x0, x1



	.if	\el == 0

	/*

arch/arm64/lib/clear_user.S

+1 −1
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ 
 * Alignment fixed up by hardware.

 */

ENTRY(__clear_user)

	uaccess_enable_not_uao x2, x3

	uaccess_enable_not_uao x2, x3, x4

	mov	x2, x1			// save the size for fixup return

	subs	x1, x1, #8

	b.mi	2f

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