From: Christoph Hellwig <hch@xxxxxx> Subject: maccess: always use strict semantics for probe_kernel_read Except for historical confusion in the kprobes/uprobes and bpf tracers, which has been fixed now, there is no good reason to ever allow user memory accesses from probe_kernel_read. Switch probe_kernel_read to only read from kernel memory. [akpm@xxxxxxxxxxxxxxxxxxxx: update it for "mm, dump_page(): do not crash with invalid mapping pointer"] Link: http://lkml.kernel.org/r/20200521152301.2587579-17-hch@xxxxxx Signed-off-by: Christoph Hellwig <hch@xxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxx> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxx> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/parisc/lib/memcpy.c | 2 - arch/um/kernel/maccess.c | 2 - arch/x86/mm/maccess.c | 9 +------ include/linux/uaccess.h | 4 --- kernel/trace/bpf_trace.c | 2 - kernel/trace/trace_kprobe.c | 4 +-- mm/debug.c | 10 ++++---- mm/maccess.c | 40 +++++----------------------------- 8 files changed, 19 insertions(+), 54 deletions(-) --- a/arch/parisc/lib/memcpy.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/arch/parisc/lib/memcpy.c @@ -57,7 +57,7 @@ void * memcpy(void * dst,const void *src EXPORT_SYMBOL(raw_copy_in_user); EXPORT_SYMBOL(memcpy); -bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict) +bool probe_kernel_read_allowed(const void *unsafe_src, size_t size) { if ((unsigned long)unsafe_src < PAGE_SIZE) return false; --- a/arch/um/kernel/maccess.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/arch/um/kernel/maccess.c @@ -7,7 +7,7 @@ #include <linux/kernel.h> #include <os.h> -bool probe_kernel_read_allowed(const void *src, size_t size, bool strict) +bool probe_kernel_read_allowed(const void *src, size_t size) { void *psrc = (void *)rounddown((unsigned long)src, PAGE_SIZE); --- a/arch/x86/mm/maccess.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/arch/x86/mm/maccess.c @@ -9,13 +9,10 @@ static __always_inline u64 canonical_add return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits); } -bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict) +bool probe_kernel_read_allowed(const void *unsafe_src, size_t size) { unsigned long vaddr = (unsigned long)unsafe_src; - if (!strict) - return true; - /* * Range covering the highest possible canonical userspace address * as well as non-canonical address range. For the canonical range @@ -25,10 +22,8 @@ bool probe_kernel_read_allowed(const voi canonical_address(vaddr, boot_cpu_data.x86_virt_bits) == vaddr; } #else -bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, bool strict) +bool probe_kernel_read_allowed(const void *unsafe_src, size_t size) { - if (!strict) - return true; return (unsigned long)unsafe_src >= TASK_SIZE_MAX; } #endif --- a/include/linux/uaccess.h~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/include/linux/uaccess.h @@ -301,11 +301,9 @@ copy_struct_from_user(void *dst, size_t return 0; } -bool probe_kernel_read_allowed(const void *unsafe_src, size_t size, - bool strict); +bool probe_kernel_read_allowed(const void *unsafe_src, size_t size); extern long probe_kernel_read(void *dst, const void *src, size_t size); -extern long probe_kernel_read_strict(void *dst, const void *src, size_t size); extern long probe_user_read(void *dst, const void __user *src, size_t size); extern long notrace probe_kernel_write(void *dst, const void *src, size_t size); --- a/kernel/trace/bpf_trace.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/kernel/trace/bpf_trace.c @@ -196,7 +196,7 @@ bpf_probe_read_kernel_common(void *dst, if (unlikely(ret < 0)) goto fail; - ret = probe_kernel_read_strict(dst, unsafe_ptr, size); + ret = probe_kernel_read(dst, unsafe_ptr, size); if (unlikely(ret < 0)) goto fail; return ret; --- a/kernel/trace/trace_kprobe.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/kernel/trace/trace_kprobe.c @@ -1222,7 +1222,7 @@ fetch_store_strlen(unsigned long addr) #endif do { - ret = probe_kernel_read_strict(&c, (u8 *)addr + len, 1); + ret = probe_kernel_read(&c, (u8 *)addr + len, 1); len++; } while (c && ret == 0 && len < MAX_STRING_SIZE); @@ -1300,7 +1300,7 @@ probe_mem_read(void *dest, void *src, si if ((unsigned long)src < TASK_SIZE) return probe_mem_read_user(dest, src, size); #endif - return probe_kernel_read_strict(dest, src, size); + return probe_kernel_read(dest, src, size); } /* Note that we don't verify it, since the code does not come from user space */ --- a/mm/debug.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/mm/debug.c @@ -120,9 +120,9 @@ void __dump_page(struct page *page, cons * mapping can be invalid pointer and we don't want to crash * accessing it, so probe everything depending on it carefully */ - if (probe_kernel_read_strict(&host, &mapping->host, - sizeof(struct inode *)) || - probe_kernel_read_strict(&a_ops, &mapping->a_ops, + if (probe_kernel_read(&host, &mapping->host, + sizeof(struct inode *)) || + probe_kernel_read(&a_ops, &mapping->a_ops, sizeof(struct address_space_operations *))) { pr_warn("failed to read mapping->host or a_ops, mapping not a valid kernel address?\n"); goto out_mapping; @@ -133,7 +133,7 @@ void __dump_page(struct page *page, cons goto out_mapping; } - if (probe_kernel_read_strict(&dentry_first, + if (probe_kernel_read(&dentry_first, &host->i_dentry.first, sizeof(struct hlist_node *))) { pr_warn("mapping->a_ops:%ps with invalid mapping->host inode address %px\n", a_ops, host); @@ -146,7 +146,7 @@ void __dump_page(struct page *page, cons } dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias); - if (probe_kernel_read_strict(&dentry, dentry_ptr, + if (probe_kernel_read(&dentry, dentry_ptr, sizeof(struct dentry))) { pr_warn("mapping->aops:%ps with invalid mapping->host->i_dentry.first %px\n", a_ops, dentry_ptr); --- a/mm/maccess.c~maccess-always-use-strict-semantics-for-probe_kernel_read +++ a/mm/maccess.c @@ -6,36 +6,13 @@ #include <linux/mm.h> #include <linux/uaccess.h> -static long __probe_kernel_read(void *dst, const void *src, size_t size, - bool strict); - -bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size, - bool strict) +bool __weak probe_kernel_read_allowed(const void *unsafe_src, size_t size) { return true; } /** - * probe_kernel_read(): safely attempt to read from any location - * @dst: pointer to the buffer that shall take the data - * @src: address to read from - * @size: size of the data chunk - * - * Same as probe_kernel_read_strict() except that for architectures with - * not fully separated user and kernel address spaces this function also works - * for user address tanges. - * - * DO NOT USE THIS FUNCTION - it is broken on architectures with entirely - * separate kernel and user address spaces, and also a bad idea otherwise. - */ -long probe_kernel_read(void *dst, const void *src, size_t size) -{ - return __probe_kernel_read(dst, src, size, false); -} -EXPORT_SYMBOL_GPL(probe_kernel_read); - -/** - * probe_kernel_read_strict(): safely attempt to read from kernel-space + * probe_kernel_read(): safely attempt to read from kernel-space * @dst: pointer to the buffer that shall take the data * @src: address to read from * @size: size of the data chunk @@ -48,18 +25,12 @@ EXPORT_SYMBOL_GPL(probe_kernel_read); * probe_kernel_read() suitable for use within regions where the caller * already holds mmap_lock, or other locks which nest inside mmap_lock. */ -long probe_kernel_read_strict(void *dst, const void *src, size_t size) -{ - return __probe_kernel_read(dst, src, size, true); -} - -static long __probe_kernel_read(void *dst, const void *src, size_t size, - bool strict) +long probe_kernel_read(void *dst, const void *src, size_t size) { long ret; mm_segment_t old_fs = get_fs(); - if (!probe_kernel_read_allowed(src, size, strict)) + if (!probe_kernel_read_allowed(src, size)) return -EFAULT; set_fs(KERNEL_DS); @@ -73,6 +44,7 @@ static long __probe_kernel_read(void *ds return -EFAULT; return 0; } +EXPORT_SYMBOL_GPL(probe_kernel_read); /** * probe_user_read(): safely attempt to read from a user-space location @@ -181,7 +153,7 @@ long strncpy_from_kernel_nofault(char *d if (unlikely(count <= 0)) return 0; - if (!probe_kernel_read_allowed(unsafe_addr, count, true)) + if (!probe_kernel_read_allowed(unsafe_addr, count)) return -EFAULT; set_fs(KERNEL_DS); _
