Merge tag 'stackleak-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull stackleak gcc plugin from Kees Cook:
 "Please pull this new GCC plugin, stackleak, for v4.20-rc1. This plugin
  was ported from grsecurity by Alexander Popov. It provides efficient
  stack content poisoning at syscall exit. This creates a defense
  against at least two classes of flaws:

   - Uninitialized stack usage. (We continue to work on improving the
     compiler to do this in other ways: e.g. unconditional zero init was
     proposed to GCC and Clang, and more plugin work has started too).

   - Stack content exposure. By greatly reducing the lifetime of valid
     stack contents, exposures via either direct read bugs or unknown
     cache side-channels become much more difficult to exploit. This
     complements the existing buddy and heap poisoning options, but
     provides the coverage for stacks.

  The x86 hooks are included in this series (which have been reviewed by
  Ingo, Dave Hansen, and Thomas Gleixner). The arm64 hooks have already
  been merged through the arm64 tree (written by Laura Abbott and
  reviewed by Mark Rutland and Will Deacon).

  With VLAs having been removed this release, there is no need for
  alloca() protection, so it has been removed from the plugin"

* tag 'stackleak-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  arm64: Drop unneeded stackleak_check_alloca()
  stackleak: Allow runtime disabling of kernel stack erasing
  doc: self-protection: Add information about STACKLEAK feature
  fs/proc: Show STACKLEAK metrics in the /proc file system
  lkdtm: Add a test for STACKLEAK
  gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack
  x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 37a679501ddc..1b8775298cf7 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -89,6 +89,7 @@ show up in /proc/sys/kernel:
 - shmmni
 - softlockup_all_cpu_backtrace
 - soft_watchdog
+- stack_erasing
 - stop-a                      [ SPARC only ]
 - sysrq                       ==> Documentation/admin-guide/sysrq.rst
 - sysctl_writes_strict
@@ -987,6 +988,23 @@ detect a hard lockup condition.
 
 ==============================================================
 
+stack_erasing
+
+This parameter can be used to control kernel stack erasing at the end
+of syscalls for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK.
+
+That erasing reduces the information which kernel stack leak bugs
+can reveal and blocks some uninitialized stack variable attacks.
+The tradeoff is the performance impact: on a single CPU system kernel
+compilation sees a 1% slowdown, other systems and workloads may vary.
+
+  0: kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
+
+  1: kernel stack erasing is enabled (default), it is performed before
+     returning to the userspace at the end of syscalls.
+
+==============================================================
+
 tainted:
 
 Non-zero if the kernel has been tainted. Numeric values, which can be