[PATCH v3 06/20] arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN

Will Deacon
2017-12-06T12:36:23Z

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: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm64/Kconfig | 1 -
arch/arm64/include/asm/asm-uaccess.h | 25 +++++++++++++++++--------
arch/arm64/include/asm/uaccess.h | 21 +++++++++++++++++----
arch/arm64/kernel/entry.S | 4 ++--
arch/arm64/lib/clear_user.S | 2 +-
arch/arm64/lib/copy_from_user.S | 2 +-
arch/arm64/lib/copy_in_user.S | 2 +-
arch/arm64/lib/copy_to_user.S | 2 +-
arch/arm64/mm/cache.S | 2 +-
arch/arm64/xen/hypercall.S | 2 +-
10 files changed, 42 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7e7d7fd152c4..a93339f5178f 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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
diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
index b3da6c886835..21b8cf304028 100644
--- a/arch/arm64/include/asm/asm-uaccess.h
+++ b/arch/arm64/include/asm/asm-uaccess.h
@@ -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
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index fc0f9eb66039..750a3b76a01c 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -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);
}
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 804e43c9cb0b..d454d8ed45e4 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -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
/*
diff --git a/arch/arm64/lib/clear_user.S b/arch/arm64/lib/clear_user.S
index e88fb99c1561..8f9c4641e706 100644
--- a/arch/arm64/lib/clear_user.S
+++ b/arch/arm64/lib/clear_user.S
@@ -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
diff --git a/arch/arm64/lib/copy_from_user.S b/arch/arm64/lib/copy_from_user.S
index 4b5d826895ff..69d86a80f3e2 100644
--- a/arch/arm64/lib/copy_from_user.S
+++ b/arch/arm64/lib/copy_from_user.S
@@ -64,7 +64,7 @@

end .req x5
ENTRY(__arch_copy_from_user)
- uaccess_enable_not_uao x3, x4
+ uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
#include "copy_template.S"
uaccess_disable_not_uao x3
diff --git a/arch/arm64/lib/copy_in_user.S b/arch/arm64/lib/copy_in_user.S
index b24a830419ad..e442b531252a 100644
--- a/arch/arm64/lib/copy_in_user.S
+++ b/arch/arm64/lib/copy_in_user.S
@@ -65,7 +65,7 @@

end .req x5
ENTRY(raw_copy_in_user)
- uaccess_enable_not_uao x3, x4
+ uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
#include "copy_template.S"
uaccess_disable_not_uao x3
diff --git a/arch/arm64/lib/copy_to_user.S b/arch/arm64/lib/copy_to_user.S
index 351f0766f7a6..318f15d5c336 100644
--- a/arch/arm64/lib/copy_to_user.S
+++ b/arch/arm64/lib/copy_to_user.S
@@ -63,7 +63,7 @@

end .req x5
ENTRY(__arch_copy_to_user)
- uaccess_enable_not_uao x3, x4
+ uaccess_enable_not_uao x3, x4, x5
add end, x0, x2
#include "copy_template.S"
uaccess_disable_not_uao x3
diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
index 7f1dbe962cf5..6cd20a8c0952 100644
--- a/arch/arm64/mm/cache.S
+++ b/arch/arm64/mm/cache.S
@@ -49,7 +49,7 @@ ENTRY(flush_icache_range)
* - end - virtual end address of region
*/
ENTRY(__flush_cache_user_range)
- uaccess_ttbr0_enable x2, x3
+ uaccess_ttbr0_enable x2, x3, x4
dcache_line_size x2, x3
sub x3, x2, #1
bic x4, x0, x3
diff --git a/arch/arm64/xen/hypercall.S b/arch/arm64/xen/hypercall.S
index 401ceb71540c..acdbd2c9e899 100644
--- a/arch/arm64/xen/hypercall.S
+++ b/arch/arm64/xen/hypercall.S
@@ -101,7 +101,7 @@ ENTRY(privcmd_call)
* need the explicit uaccess_enable/disable if the TTBR0 PAN emulation
* is enabled (it implies that hardware UAO and PAN disabled).
*/
- uaccess_ttbr0_enable x6, x7
+ uaccess_ttbr0_enable x6, x7, x8
hvc XEN_IMM

/*
--
2.1.4