Add probe_user_read() and strncpy_from_unsafe_user() which allows caller to access user-space in IRQ context.
Current probe_kernel_read() and strncpy_from_unsafe() are not available for user-space memory, because it sets KERNEL_DS while accessing data. On some arch, user address space and kernel address space can be co-exist, but others can not. In that case, setting KERNEL_DS means given address is treated as a kernel address space. To access user-space memory without pagefault, we need these new functions which sets USER_DS while accessing the data. Signed-off-by: Masami Hiramatsu <mhira...@kernel.org> --- Changes in v3: - Use user_access_ok() for probe_user_read(). Changes in v2: - Simplify strncpy_from_unsafe_user() using strncpy_from_user() according to Linus's suggestion. - Simplify probe_user_read() not using intermediate function. --- include/linux/uaccess.h | 13 +++++++ mm/maccess.c | 94 ++++++++++++++++++++++++++++++++++++++++++++--- 2 files changed, 101 insertions(+), 6 deletions(-) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 1afd9dfabe67..598a96210d04 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -258,6 +258,17 @@ extern long probe_kernel_read(void *dst, const void *src, size_t size); extern long __probe_kernel_read(void *dst, const void *src, size_t size); /* + * probe_user_read(): safely attempt to read from a location in user space + * @dst: pointer to the buffer that shall take the data + * @src: address to read from + * @size: size of the data chunk + * + * Safely read from address @src to the buffer at @dst. If a kernel fault + * happens, handle that and return -EFAULT. + */ +extern long probe_user_read(void *dst, const void __user *src, size_t size); + +/* * probe_kernel_write(): safely attempt to write to a location * @dst: address to write to * @src: pointer to the data that shall be written @@ -270,6 +281,8 @@ extern long notrace probe_kernel_write(void *dst, const void *src, size_t size); extern long notrace __probe_kernel_write(void *dst, const void *src, size_t size); extern long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count); +extern long strncpy_from_unsafe_user(char *dst, const void __user *unsafe_addr, + long count); /** * probe_kernel_address(): safely attempt to read from a location diff --git a/mm/maccess.c b/mm/maccess.c index ec00be51a24f..b24df3e731c8 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -5,8 +5,20 @@ #include <linux/mm.h> #include <linux/uaccess.h> +static __always_inline long +probe_read_common(void *dst, const void __user *src, size_t size) +{ + long ret; + + pagefault_disable(); + ret = __copy_from_user_inatomic(dst, src, size); + pagefault_enable(); + + return ret ? -EFAULT : 0; +} + /** - * probe_kernel_read(): safely attempt to read from a location + * probe_kernel_read(): safely attempt to read from a kernel-space location * @dst: pointer to the buffer that shall take the data * @src: address to read from * @size: size of the data chunk @@ -29,17 +41,47 @@ long __probe_kernel_read(void *dst, const void *src, size_t size) mm_segment_t old_fs = get_fs(); set_fs(KERNEL_DS); - pagefault_disable(); - ret = __copy_from_user_inatomic(dst, - (__force const void __user *)src, size); - pagefault_enable(); + ret = probe_read_common(dst, (__force const void __user *)src, size); set_fs(old_fs); - return ret ? -EFAULT : 0; + return ret; } EXPORT_SYMBOL_GPL(probe_kernel_read); /** + * probe_user_read(): safely attempt to read from a user-space location + * @dst: pointer to the buffer that shall take the data + * @src: address to read from. This must be a user address. + * @size: size of the data chunk + * + * Safely read from user address @src to the buffer at @dst. If a kernel fault + * happens, handle that and return -EFAULT. + */ + +long __weak probe_user_read(void *dst, const void __user *src, size_t size) + __attribute__((alias("__probe_user_read"))); + +long __probe_user_read(void *dst, const void __user *src, size_t size) +{ + long ret; + mm_segment_t old_fs = get_fs(); + + /* + * Since this can be called in IRQ context, we carefully set the + * USER_DS and use user_access_ok() which checks segment setting + * instead of task context. + */ + set_fs(USER_DS); + if (!user_access_ok(src, size)) + ret = -EFAULT; + else + ret = probe_read_common(dst, src, size); + set_fs(old_fs); + return ret; +} +EXPORT_SYMBOL_GPL(probe_user_read); + +/** * probe_kernel_write(): safely attempt to write to a location * @dst: address to write to * @src: pointer to the data that shall be written @@ -66,6 +108,7 @@ long __probe_kernel_write(void *dst, const void *src, size_t size) } EXPORT_SYMBOL_GPL(probe_kernel_write); + /** * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. * @dst: Destination address, in kernel space. This buffer must be at @@ -105,3 +148,42 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) return ret ? -EFAULT : src - unsafe_addr; } + +/** + * strncpy_from_unsafe_user: - Copy a NUL terminated string from unsafe user + * address. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @unsafe_addr: Unsafe user address. + * @count: Maximum number of bytes to copy, including the trailing NUL. + * + * Copies a NUL-terminated string from unsafe user address to kernel buffer. + * + * On success, returns the length of the string INCLUDING the trailing NUL. + * + * If access fails, returns -EFAULT (some data may have been copied + * and the trailing NUL added). + * + * If @count is smaller than the length of the string, copies @count-1 bytes, + * sets the last byte of @dst buffer to NUL and returns @count. + */ +long strncpy_from_unsafe_user(char *dst, const void __user *src, long count) +{ + mm_segment_t old_fs = get_fs(); + long ret; + + if (unlikely(count <= 0)) + return 0; + + set_fs(USER_DS); + pagefault_disable(); + ret = strncpy_from_user(dst, src, count); + pagefault_enable(); + set_fs(old_fs); + if (ret >= count) { + ret = count; + dst[ret - 1] = '\0'; + } else if (ret > 0) + ret++; + return ret; +}