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stack: Introduce CONFIG_RANDOMIZE_KSTACK_OFFSET

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The randomize_kstack_offset feature is unconditionally compiled in when
the architecture supports it.

To add constraints on compiler versions, we require a dedicated Kconfig
variable. Therefore, introduce RANDOMIZE_KSTACK_OFFSET.

Furthermore, this option is now also configurable by EXPERT kernels:
while the feature is supposed to have zero performance overhead when
disabled, due to its use of static branches, there are few cases where
giving a distribution the option to disable the feature entirely makes
sense. For example, in very resource constrained environments, which
would never enable the feature to begin with, in which case the
additional kernel code size increase would be redundant.

Signed-off-by: Marco Elver <elver@google.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220131090521.1947110-1-elver@google.com
This commit is contained in:
Marco Elver
2022-01-31 10:05:20 +01:00
committed by Kees Cook
parent ae978009fc
commit 8cb37a5974
3 changed files with 24 additions and 6 deletions
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5
include/linux/randomize_kstack.h
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@@ -2,6 +2,7 @@
#ifndef _LINUX_RANDOMIZE_KSTACK_H
#define _LINUX_RANDOMIZE_KSTACK_H
#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
#include <linux/kernel.h>
#include <linux/jump_label.h>
#include <linux/percpu-defs.h>
@@ -50,5 +51,9 @@ void *__builtin_alloca(size_t size);
raw_cpu_write(kstack_offset, offset); \
} \
} while (0)
#else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
#define add_random_kstack_offset() do { } while (0)
#define choose_random_kstack_offset(rand) do { } while (0)
#endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
#endif