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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