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Message-Id: <1507157703-14972-4-git-send-email-alex.popov@linux.com>
Date: Thu, 5 Oct 2017 01:55:03 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
keescook@...omium.org,
pageexec@...email.hu,
spender@...ecurity.net,
tycho@...ker.com,
Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Andy Lutomirski <luto@...capital.net>,
x86@...nel.org,
alex.popov@...ux.com
Subject: [PATCH RFC v4 3/3] doc: self-protection: Add information about STACKLEAK feature
Add information about STACKLEAK feature to "Stack depth overflow" and
"Memory poisoning" sections of self-protection.rst.
Signed-off-by: Alexander Popov <alex.popov@...ux.com>
---
Documentation/security/self-protection.rst | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/Documentation/security/self-protection.rst b/Documentation/security/self-protection.rst
index 60c8bd8..9693a90 100644
--- a/Documentation/security/self-protection.rst
+++ b/Documentation/security/self-protection.rst
@@ -165,10 +165,15 @@ Stack depth overflow
A less well understood attack is using a bug that triggers the
kernel to consume stack memory with deep function calls or large stack
allocations. With this attack it is possible to write beyond the end of
-the kernel's preallocated stack space and into sensitive structures. Two
-important changes need to be made for better protections: moving the
-sensitive thread_info structure elsewhere, and adding a faulting memory
-hole at the bottom of the stack to catch these overflows.
+the kernel's preallocated stack space and into sensitive structures.
+The combination of the following measures gives better protection:
+
+* moving the sensitive thread_info structure off the stack
+ (``CONFIG_THREAD_INFO_IN_TASK``);
+* adding a faulting memory hole at the bottom of the stack to catch
+ these overflows (``CONFIG_VMAP_STACK``);
+* runtime checking that alloca() calls don't overstep the stack boundary
+ (``CONFIG_GCC_PLUGIN_STACKLEAK``).
Heap memory integrity
---------------------
@@ -287,11 +292,11 @@ sure structure holes are cleared.
Memory poisoning
----------------
-When releasing memory, it is best to poison the contents (clear stack on
-syscall return, wipe heap memory on a free), to avoid reuse attacks that
-rely on the old contents of memory. This frustrates many uninitialized
-variable attacks, stack content exposures, heap content exposures, and
-use-after-free attacks.
+When releasing memory, it is best to poison the contents, to avoid reuse
+attacks that rely on the old contents of memory. E.g., clear stack on a
+syscall return (``CONFIG_GCC_PLUGIN_STACKLEAK``), wipe heap memory on a
+free. This frustrates many uninitialized variable attacks, stack content
+exposures, heap content exposures, and use-after-free attacks.
Destination tracking
--------------------
--
2.7.4
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