Re: [PATCH 1/2] signal: Factor copy_siginfo_to_external32 from copy_siginfo_to_user32
From: Christophe Leroy
Date: Sun Apr 19 2020 - 05:47:11 EST
Le 19/04/2020 Ã 10:13, Christoph Hellwig a ÃcritÂ:
On Sat, Apr 18, 2020 at 06:55:56AM -0500, Eric W. Biederman wrote:
Is that really an issue to use that set_fs() in the coredump code ?
Using set_fs() is pretty bad and something that we would like to remove
from the kernel entirely. The fewer instances of set_fs() we have the
better.
I forget all of the details but set_fs() is both a type violation and an
attack point when people are attacking the kernel. The existence of
set_fs() requires somethings that should be constants to be variables.
Something about that means that our current code is difficult to protect
from spectre style vulnerabilities.
Yes, set_fs requires variable based address checking in the uaccess
routines for architectures with a shared address space, or even entirely
different code for architectures with separate kernel and user address
spaces. My plan is to hopefully kill set_fs in its current form a few
merge windows down the road. We'll probably still need some form of
it to e.g. mark a thread as kernel thread vs also being able to execute
user code, but it will be much ore limited than before, called from very
few places and actually be a no-op for many architectures.
Oh nice. Some time ago I proposed a patch to change set_fs() to a
flip/flop flag based logic, see
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/dd2876b808ea38eb7b7f760ecd6ce06096c61fb5.1580295551.git.christophe.leroy@xxxxxx/
But if we manage to get rid of it completely, that's even better.