Add probe_user_read() and strncpy_from_unsafe_user() which will not involves mm_sem so we can use it for accessing user-space in irq-handler.
Signed-off-by: Masami Hiramatsu <[email protected]> --- include/linux/uaccess.h | 13 +++++ mm/maccess.c | 134 +++++++++++++++++++++++++++++++++++++++++------ 2 files changed, 131 insertions(+), 16 deletions(-) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 37b226e8df13..906573b8f02c 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -240,6 +240,17 @@ 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 @@ -252,6 +263,8 @@ 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 7a9752d59587..7d38d783e0b1 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 @@ -30,18 +42,53 @@ long __probe_kernel_read(void *dst, const void *src, size_t size) set_fs(KERNEL_DS); current->kernel_uaccess_faults_ok++; - 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); current->kernel_uaccess_faults_ok--; 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"))); + +static long __normal_probe_user_read(void *dst, const void __user *src, + size_t size) +{ + if (!access_ok(src, size)) + return -EFAULT; + + return probe_read_common(dst, src, size); +} + +long __probe_user_read(void *dst, const void __user *src, size_t size) +{ + long ret; + mm_segment_t old_fs = get_fs(); + + if (segment_eq(old_fs, USER_DS)) { + ret = __normal_probe_user_read(dst, src, size); + } else { + set_fs(USER_DS); + ret = __normal_probe_user_read(dst, src, size); + set_fs(old_fs); + } + return ret ? -EFAULT : 0; +} +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 @@ -70,6 +117,22 @@ long __probe_kernel_write(void *dst, const void *src, size_t size) } EXPORT_SYMBOL_GPL(probe_kernel_write); + +static __always_inline long strncpy_from_unsafe_common(char *dst, + const char __user *unsafe_addr, long count) +{ + const char __user *src = unsafe_addr; + int ret; + + pagefault_disable(); + do { + ret = __get_user(*dst++, src++); + } while (dst[-1] && ret == 0 && src - unsafe_addr < count); + dst[-1] = '\0'; + pagefault_enable(); + + return ret ? -EFAULT : src - unsafe_addr; +} /** * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. * @dst: Destination address, in kernel space. This buffer must be at @@ -90,7 +153,6 @@ EXPORT_SYMBOL_GPL(probe_kernel_write); long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) { mm_segment_t old_fs = get_fs(); - const void *src = unsafe_addr; long ret; if (unlikely(count <= 0)) @@ -98,16 +160,56 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) set_fs(KERNEL_DS); current->kernel_uaccess_faults_ok++; - pagefault_disable(); - - do { - ret = __get_user(*dst++, (const char __user __force *)src++); - } while (dst[-1] && ret == 0 && src - unsafe_addr < count); - - dst[-1] = '\0'; - pagefault_enable(); + ret = strncpy_from_unsafe_common(dst, + (const char __user __force *)unsafe_addr, count); current->kernel_uaccess_faults_ok--; set_fs(old_fs); - return ret ? -EFAULT : src - unsafe_addr; + return ret; +} + +static __always_inline long __strncpy_from_unsafe_user(char *dst, + const char __user *unsafe_addr, long count) +{ + if (!access_ok(unsafe_addr, count)) + return -EFAULT; + + return strncpy_from_unsafe_common(dst, unsafe_addr, count); +} + +/** + * 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 *unsafe_addr, + long count) +{ + mm_segment_t old_fs = get_fs(); + long ret; + + if (unlikely(count <= 0)) + return 0; + + if (segment_eq(old_fs, USER_DS)) { + ret = __strncpy_from_unsafe_user(dst, unsafe_addr, count); + } else { + set_fs(USER_DS); + ret = __strncpy_from_unsafe_user(dst, unsafe_addr, count); + set_fs(old_fs); + } + return ret; }
