[PATCHv3 16/17] arm64: uaccess: remove redundant PAN toggling

Mark Rutland
2020-10-26T13:40:24Z

Some code (e.g. futex) needs to make privileged accesses to userspace
memory, and uses uaccess_{enable,disable}_privileged() in order to
permit this. All other uaccess primitives use LDTR/STTR, and never need
to toggle PAN.

Remove the redundant PAN toggling.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
---
arch/arm64/include/asm/cpucaps.h | 1 -
arch/arm64/include/asm/uaccess.h | 59 +++++++++++++---------------------------
arch/arm64/kernel/cpufeature.c | 17 ------------
3 files changed, 19 insertions(+), 58 deletions(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 42868dbd29fd9..e3a7b6fe98d23 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -17,7 +17,6 @@
#define ARM64_WORKAROUND_834220 7
#define ARM64_HAS_NO_HW_PREFETCH 8
#define ARM64_HAS_UAO 9
-#define ARM64_ALT_PAN_NOT_UAO 10
#define ARM64_HAS_VIRT_HOST_EXTN 11
#define ARM64_WORKAROUND_CAVIUM_27456 12
#define ARM64_HAS_32BIT_EL0 13
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 9223c74b4f5a8..d9741a58953d1 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -159,41 +159,20 @@ static inline void __uaccess_enable_hw_pan(void)
CONFIG_ARM64_PAN));
}

-#define __uaccess_disable(alt) \
-do { \
- if (!uaccess_ttbr0_disable()) \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), alt, \
- CONFIG_ARM64_PAN)); \
-} while (0)
-
-#define __uaccess_enable(alt) \
-do { \
- if (!uaccess_ttbr0_enable()) \
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), alt, \
- CONFIG_ARM64_PAN)); \
-} while (0)
-
static inline void uaccess_disable_privileged(void)
{
- __uaccess_disable(ARM64_HAS_PAN);
-}
+ if (uaccess_ttbr0_disable())
+ return;

-static inline void uaccess_enable_privileged(void)
-{
- __uaccess_enable(ARM64_HAS_PAN);
+ __uaccess_enable_hw_pan();
}

-/*
- * These functions are no-ops when UAO is present.
- */
-static inline void uaccess_disable_not_uao(void)
+static inline void uaccess_enable_privileged(void)
{
- __uaccess_disable(ARM64_ALT_PAN_NOT_UAO);
-}
+ if (uaccess_ttbr0_enable())
+ return;

-static inline void uaccess_enable_not_uao(void)
-{
- __uaccess_enable(ARM64_ALT_PAN_NOT_UAO);
+ __uaccess_disable_hw_pan();
}

/*
@@ -265,9 +244,9 @@ do { \

#define __raw_get_user(x, ptr, err) \
do { \
- uaccess_enable_not_uao(); \
+ uaccess_ttbr0_enable(); \
__raw_get_mem("ldtr", x, ptr, err); \
- uaccess_disable_not_uao(); \
+ uaccess_ttbr0_disable(); \
} while (0)

#define __get_user_error(x, ptr, err) \
@@ -338,9 +317,9 @@ do { \

#define __raw_put_user(x, ptr, err) \
do { \
- uaccess_enable_not_uao(); \
+ uaccess_ttbr0_enable(); \
__raw_put_mem("sttr", x, ptr, err); \
- uaccess_disable_not_uao(); \
+ uaccess_ttbr0_disable(); \
} while (0)

#define __put_user_error(x, ptr, err) \
@@ -378,10 +357,10 @@ extern unsigned long __must_check __arch_copy_from_user(void *to, const void __u
#define raw_copy_from_user(to, from, n) \
({ \
unsigned long __acfu_ret; \
- uaccess_enable_not_uao(); \
+ uaccess_ttbr0_enable(); \
__acfu_ret = __arch_copy_from_user((to), \
__uaccess_mask_ptr(from), (n)); \
- uaccess_disable_not_uao(); \
+ uaccess_ttbr0_disable(); \
__acfu_ret; \
})

@@ -389,10 +368,10 @@ extern unsigned long __must_check __arch_copy_to_user(void __user *to, const voi
#define raw_copy_to_user(to, from, n) \
({ \
unsigned long __actu_ret; \
- uaccess_enable_not_uao(); \
+ uaccess_ttbr0_enable(); \
__actu_ret = __arch_copy_to_user(__uaccess_mask_ptr(to), \
(from), (n)); \
- uaccess_disable_not_uao(); \
+ uaccess_ttbr0_disable(); \
__actu_ret; \
})

@@ -400,10 +379,10 @@ extern unsigned long __must_check __arch_copy_in_user(void __user *to, const voi
#define raw_copy_in_user(to, from, n) \
({ \
unsigned long __aciu_ret; \
- uaccess_enable_not_uao(); \
+ uaccess_ttbr0_enable(); \
__aciu_ret = __arch_copy_in_user(__uaccess_mask_ptr(to), \
__uaccess_mask_ptr(from), (n)); \
- uaccess_disable_not_uao(); \
+ uaccess_ttbr0_disable(); \
__aciu_ret; \
})

@@ -414,9 +393,9 @@ extern unsigned long __must_check __arch_clear_user(void __user *to, unsigned lo
static inline unsigned long __must_check __clear_user(void __user *to, unsigned long n)
{
if (access_ok(to, n)) {
- uaccess_enable_not_uao();
+ uaccess_ttbr0_enable();
n = __arch_clear_user(__uaccess_mask_ptr(to), n);
- uaccess_disable_not_uao();
+ uaccess_ttbr0_disable();
}
return n;
}
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 5e9732f3561ec..5d7032625ff2b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -153,10 +153,6 @@ EXPORT_SYMBOL(cpu_hwcap_keys);
.width = 0, \
}

-/* meta feature for alternatives */
-static bool __maybe_unused
-cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused);
-
static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);

static bool __system_matches_cap(unsigned int n);
@@ -1779,13 +1775,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.min_field_value = 1,
},
#endif /* CONFIG_ARM64_UAO */
-#ifdef CONFIG_ARM64_PAN
- {
- .capability = ARM64_ALT_PAN_NOT_UAO,
- .type = ARM64_CPUCAP_SYSTEM_FEATURE,
- .matches = cpufeature_pan_not_uao,
- },
-#endif /* CONFIG_ARM64_PAN */
#ifdef CONFIG_ARM64_VHE
{
.desc = "Virtualization Host Extensions",
@@ -2726,12 +2715,6 @@ void __init setup_cpu_features(void)
ARCH_DMA_MINALIGN);
}

-static bool __maybe_unused
-cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused)
-{
- return (__system_matches_cap(ARM64_HAS_PAN) && !__system_matches_cap(ARM64_HAS_UAO));
-}
-
static void __maybe_unused cpu_enable_cnp(struct arm64_cpu_capabilities const *cap)
{
cpu_replace_ttbr1(lm_alias(swapper_pg_dir));