From 0ab32b6f1b88444524e52429fab334ff96683a3f Mon Sep 17 00:00:00 2001 From: Andrew Morton Date: Thu, 5 Nov 2015 18:46:03 -0800 Subject: uaccess: reimplement probe_kernel_address() using probe_kernel_read() probe_kernel_address() is basically the same as the (later added) probe_kernel_read(). The return value on EFAULT is a bit different: probe_kernel_address() returns number-of-bytes-not-copied whereas probe_kernel_read() returns -EFAULT. All callers have been checked, none cared. probe_kernel_read() can be overridden by the architecture whereas probe_kernel_address() cannot. parisc, blackfin and um do this, to insert additional checking. Hence this patch possibly fixes obscure bugs, although there are only two probe_kernel_address() callsites outside arch/. My first attempt involved removing probe_kernel_address() entirely and converting all callsites to use probe_kernel_read() directly, but that got tiresome. This patch shrinks mm/slab_common.o by 218 bytes. For a single probe_kernel_address() callsite. Cc: Steven Miao Cc: Jeff Dike Cc: Richard Weinberger Cc: "James E.J. Bottomley" Cc: Helge Deller Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/maccess.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'mm/maccess.c') diff --git a/mm/maccess.c b/mm/maccess.c index 34fe24759ed1..1b13638d238d 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -13,6 +13,11 @@ * * Safely read from address @src to the buffer at @dst. If a kernel fault * happens, handle that and return -EFAULT. + * + * We ensure that the copy_from_user is executed in atomic context so that + * do_page_fault() doesn't attempt to take mmap_sem. This makes + * probe_kernel_read() suitable for use within regions where the caller + * already holds mmap_sem, or other locks which nest inside mmap_sem. */ long __weak probe_kernel_read(void *dst, const void *src, size_t size) -- cgit v1.2.3-55-g7522