diff options
| author | Kees Cook <keescook@chromium.org> | 2017-12-01 13:19:39 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-12-18 15:59:17 +0100 |
| commit | 22ec1a2aea73b9dfe340dff7945bd85af4cc6280 (patch) | |
| tree | 92c1a38f121417e5702fe1f41ef99ea1004273ae | |
| parent | d9cc5a0edb705ced4ce91b4c6ee73ec6f5bfa49a (diff) | |
/dev/mem: Add bounce buffer for copy-out
As done for /proc/kcore in
commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
this adds a bounce buffer when reading memory via /dev/mem. This
is needed to allow kernel text memory to be read out when built with
CONFIG_HARDENED_USERCOPY (which refuses to read out kernel text) and
without CONFIG_STRICT_DEVMEM (which would have refused to read any RAM
contents at all).
Since this build configuration isn't common (most systems with
CONFIG_HARDENED_USERCOPY also have CONFIG_STRICT_DEVMEM), this also tries
to inform Kconfig about the recommended settings.
This patch is modified from Brad Spengler/PaX Team's changes to /dev/mem
code in the last public patch of grsecurity/PaX based on my understanding
of the code. Changes or omissions from the original code are mine and
don't reflect the original grsecurity/PaX code.
Reported-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Fixes: f5509cc18daa ("mm: Hardened usercopy")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/char/mem.c | 27 | ||||
| -rw-r--r-- | security/Kconfig | 1 |
2 files changed, 23 insertions, 5 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 6aefe5370e5b..052011bcf100 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -107,6 +107,8 @@ static ssize_t read_mem(struct file *file, char __user *buf, phys_addr_t p = *ppos; ssize_t read, sz; void *ptr; + char *bounce; + int err; if (p != *ppos) return 0; @@ -129,15 +131,22 @@ static ssize_t read_mem(struct file *file, char __user *buf, } #endif + bounce = kmalloc(PAGE_SIZE, GFP_KERNEL); + if (!bounce) + return -ENOMEM; + while (count > 0) { unsigned long remaining; int allowed; sz = size_inside_page(p, count); + err = -EPERM; allowed = page_is_allowed(p >> PAGE_SHIFT); if (!allowed) - return -EPERM; + goto failed; + + err = -EFAULT; if (allowed == 2) { /* Show zeros for restricted memory. */ remaining = clear_user(buf, sz); @@ -149,24 +158,32 @@ static ssize_t read_mem(struct file *file, char __user *buf, */ ptr = xlate_dev_mem_ptr(p); if (!ptr) - return -EFAULT; - - remaining = copy_to_user(buf, ptr, sz); + goto failed; + err = probe_kernel_read(bounce, ptr, sz); unxlate_dev_mem_ptr(p, ptr); + if (err) + goto failed; + + remaining = copy_to_user(buf, bounce, sz); } if (remaining) - return -EFAULT; + goto failed; buf += sz; p += sz; count -= sz; read += sz; } + kfree(bounce); *ppos += read; return read; + +failed: + kfree(bounce); + return err; } static ssize_t write_mem(struct file *file, const char __user *buf, diff --git a/security/Kconfig b/security/Kconfig index e8e449444e65..3b4effd8bbc2 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -143,6 +143,7 @@ config HARDENED_USERCOPY bool "Harden memory copies between kernel and userspace" depends on HAVE_HARDENED_USERCOPY_ALLOCATOR select BUG + imply STRICT_DEVMEM help This option checks for obviously wrong memory regions when copying memory to/from the kernel (via copy_to_user() and |