arm64: uaccess: remove redundant PAN toggling

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: Christoph Hellwig <hch@lst.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201202131558.39270-12-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 64ea0bb9f42099f876abdbc48349fce6e09b0174..ab3bec7a5a4d19f49edd3c4623799d670792a96f 100644 (file)
--- 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 e639d8b2b38d9f46e0aedad9186d10a9c1e9463a..769cad7b49104389d3cbed6e855f4ee235dd8f7f 100644 (file)
--- 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 {                                                                   \
        __chk_user_ptr(ptr);                                            \
-       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 {                                                                   \
        __chk_user_ptr(ptr);                                            \
-       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 ddca55fb79f529537c8c3164581586f8bb1486ad..d09bdc60a8e32812323c45dd9bb6cde6818cbd37 100644 (file)
--- 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",
@@ -2736,12 +2725,6 @@ 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));