[PATCH 2/3] arm64: Add support for sub-page faults user probing
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2021-11-24 19:20:39
Also in:
linux-arm-kernel, linux-fsdevel, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
With MTE, even if the pte allows an access, a mismatched tag somewhere within a page can still cause a fault. Select ARCH_HAS_SUBPAGE_FAULTS if MTE is enabled and implement probe_user_writeable(). Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/uaccess.h | 33 ++++++++++++++++++++++++++++++++ 2 files changed, 34 insertions(+)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index c4207cf9bb17..dff89fd0d817 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig@@ -1777,6 +1777,7 @@ config ARM64_MTE depends on AS_HAS_LSE_ATOMICS # Required for tag checking in the uaccess routines depends on ARM64_PAN + select ARCH_HAS_SUBPAGE_FAULTS select ARCH_USES_HIGH_VMA_FLAGS help Memory Tagging (part of the ARMv8.5 Extensions) provides
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 6e2e0b7031ab..4bf947e9f9bf 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h@@ -445,4 +445,37 @@ static inline int __copy_from_user_flushcache(void *dst, const void __user *src, } #endif +#ifdef CONFIG_ARCH_HAS_SUBPAGE_FAULTS +static inline size_t __mte_probe_user_range(const char __user *uaddr, + size_t size) +{ + const char __user *end = uaddr + size; + int err = 0; + char val; + + uaddr = PTR_ALIGN_DOWN(uaddr, MTE_GRANULE_SIZE); + while (uaddr < end) { + /* + * A read is sufficient for MTE, the caller should have probed + * for the pte write permission. + */ + __raw_get_user(val, uaddr, err); + if (err) + return end - uaddr; + uaddr += MTE_GRANULE_SIZE; + } + (void)val; + + return 0; +} + +static inline size_t probe_user_writable(const void __user *uaddr, + size_t size) +{ + if (!system_supports_mte()) + return 0; + return __mte_probe_user_range(uaddr, size); +} +#endif /* CONFIG_ARCH_HAS_SUBPAGE_FAULTS */ + #endif /* __ASM_UACCESS_H */