From f3ba50a7a100e91b0b13ca43190a66c1bfdb9993 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Sat, 23 Apr 2022 11:07:50 +0100 Subject: [PATCH] arm64: Add support for user sub-page fault probing 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 the probe_subpage_writeable() function. Note that get_user() is sufficient for the writeable MTE check since the same tag mismatch fault would be triggered by a read. The caller of probe_subpage_writeable() will need to check the pte permissions (put_user, GUP). Signed-off-by: Catalin Marinas Cc: Will Deacon Link: https://lore.kernel.org/r/20220423100751.1870771-3-catalin.marinas@arm.com Signed-off-by: Catalin Marinas --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/mte.h | 1 + arch/arm64/include/asm/uaccess.h | 15 +++++++++++++++ arch/arm64/kernel/mte.c | 30 ++++++++++++++++++++++++++++++ 4 files changed, 47 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 57c4c99..290b882 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1871,6 +1871,7 @@ 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/mte.h b/arch/arm64/include/asm/mte.h index adcb937..aa52359 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -47,6 +47,7 @@ long set_mte_ctrl(struct task_struct *task, unsigned long arg); long get_mte_ctrl(struct task_struct *task); int mte_ptrace_copy_tags(struct task_struct *child, long request, unsigned long addr, unsigned long data); +size_t mte_probe_user_range(const char __user *uaddr, size_t size); #else /* CONFIG_ARM64_MTE */ diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h index e8dce0c..63f9c82 100644 --- a/arch/arm64/include/asm/uaccess.h +++ b/arch/arm64/include/asm/uaccess.h @@ -460,4 +460,19 @@ static inline int __copy_from_user_flushcache(void *dst, const void __user *src, } #endif +#ifdef CONFIG_ARCH_HAS_SUBPAGE_FAULTS + +/* + * Return 0 on success, the number of bytes not probed otherwise. + */ +static inline size_t probe_subpage_writeable(const char __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 */ diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 78b3e0f..35697a09 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include @@ -543,3 +544,32 @@ static int register_mte_tcf_preferred_sysctl(void) return 0; } subsys_initcall(register_mte_tcf_preferred_sysctl); + +/* + * Return 0 on success, the number of bytes not probed otherwise. + */ +size_t mte_probe_user_range(const char __user *uaddr, size_t size) +{ + const char __user *end = uaddr + size; + int err = 0; + char val; + + __raw_get_user(val, uaddr, err); + if (err) + return size; + + uaddr = PTR_ALIGN(uaddr, MTE_GRANULE_SIZE); + while (uaddr < end) { + /* + * A read is sufficient for mte, the caller should have probed + * for the pte write permission if required. + */ + __raw_get_user(val, uaddr, err); + if (err) + return end - uaddr; + uaddr += MTE_GRANULE_SIZE; + } + (void)val; + + return 0; +} -- 2.7.4