linux/arch/parisc
Linus Torvalds 0c389d89ab maccess: make get_kernel_nofault() check for minimal type compatibility
Now that we've renamed probe_kernel_address() to get_kernel_nofault()
and made it look and behave more in line with get_user(), some of the
subtle type behavior differences end up being more obvious and possibly
dangerous.

When you do

        get_user(val, user_ptr);

the type of the access comes from the "user_ptr" part, and the above
basically acts as

        val = *user_ptr;

by design (except, of course, for the fact that the actual dereference
is done with a user access).

Note how in the above case, the type of the end result comes from the
pointer argument, and then the value is cast to the type of 'val' as
part of the assignment.

So the type of the pointer is ultimately the more important type both
for the access itself.

But 'get_kernel_nofault()' may now _look_ similar, but it behaves very
differently.  When you do

        get_kernel_nofault(val, kernel_ptr);

it behaves like

        val = *(typeof(val) *)kernel_ptr;

except, of course, for the fact that the actual dereference is done with
exception handling so that a faulting access is suppressed and returned
as the error code.

But note how different the casting behavior of the two superficially
similar accesses are: one does the actual access in the size of the type
the pointer points to, while the other does the access in the size of
the target, and ignores the pointer type entirely.

Actually changing get_kernel_nofault() to act like get_user() is almost
certainly the right thing to do eventually, but in the meantime this
patch adds logit to at least verify that the pointer type is compatible
with the type of the result.

In many cases, this involves just casting the pointer to 'void *' to
make it obvious that the type of the pointer is not the important part.
It's not how 'get_user()' acts, but at least the behavioral difference
is now obvious and explicit.

Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-18 12:10:37 -07:00
..
boot parisc: use -fno-strict-aliasing for decompressor 2020-05-10 22:46:19 +02:00
configs parisc: Regenerate parisc defconfigs 2020-02-03 22:38:12 +01:00
include mm: consolidate pte_index() and pte_offset_*() definitions 2020-06-09 09:39:14 -07:00
kernel maccess: make get_kernel_nofault() check for minimal type compatibility 2020-06-18 12:10:37 -07:00
lib maccess: rename probe_kernel_{read,write} to copy_{from,to}_kernel_nofault 2020-06-17 10:57:41 -07:00
math-emu Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough for clang 2019-08-10 12:45:37 -07:00
mm mmap locking API: convert mmap_sem API comments 2020-06-09 09:39:14 -07:00
oprofile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
Kconfig.debug Kconfig: consolidate the "Kernel hacking" menu 2018-08-02 08:06:48 +09:00
Makefile kbuild: fix broken builds because of GZIP,BZIP2,LZOP variables 2020-06-11 20:14:41 +09:00
defpalo.conf parisc: switch to gzip-compressed vmlinuz kernel 2013-07-09 22:09:20 +02:00
install.sh parisc: make "make install" not depend on vmlinux 2013-11-07 22:28:06 +01:00
nm