kernel/sys.c: fix potential Spectre v1 issue
authorGustavo A. R. Silva <gustavo@embeddedor.com>
Fri, 25 May 2018 21:47:57 +0000 (14:47 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 26 May 2018 01:12:11 +0000 (18:12 -0700)
commit23d6aef74da86a33fa6bb75f79565e0a16ee97c2
tree553228677345d3d48ebd0d795ef69dfa00871ede
parenta21558618c5dfc55b6086743a88ce5a9c1588f0a
kernel/sys.c: fix potential Spectre v1 issue

`resource' can be controlled by user-space, hence leading to a potential
exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

  kernel/sys.c:1474 __do_compat_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap)
  kernel/sys.c:1455 __do_sys_old_getrlimit() warn: potential spectre issue 'get_current()->signal->rlim' (local cap)

Fix this by sanitizing *resource* before using it to index
current->signal->rlim

Notice that given that speculation windows are large, the policy is to
kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Link: http://lkml.kernel.org/r/20180515030038.GA11822@embeddedor.com
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/sys.c