mirror of
https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9.git
synced 2026-09-10 00:22:43 +08:00
Chris von Recklinghausen
cbe61b95fc
JIRA: https://issues.redhat.com/browse/RHEL-37308
CVE: CVE-2024-35918
commit 9c573cd313433f6c1f7236fe64b9b743500c1628
Author: Kees Cook <keescook@chromium.org>
Date: Sat Mar 9 12:24:48 2024 -0800
randomize_kstack: Improve entropy diffusion
The kstack_offset variable was really only ever using the low bits for
kernel stack offset entropy. Add a ror32() to increase bit diffusion.
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 39218ff4c6 ("stack: Optionally randomize kernel stack offset each syscall")
Link: https://lore.kernel.org/r/20240309202445.work.165-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>
60 lines
2.2 KiB
C
60 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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#ifndef _LINUX_RANDOMIZE_KSTACK_H
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#define _LINUX_RANDOMIZE_KSTACK_H
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#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
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#include <linux/kernel.h>
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#include <linux/jump_label.h>
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#include <linux/percpu-defs.h>
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DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT,
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randomize_kstack_offset);
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DECLARE_PER_CPU(u32, kstack_offset);
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/*
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* Do not use this anywhere else in the kernel. This is used here because
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* it provides an arch-agnostic way to grow the stack with correct
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* alignment. Also, since this use is being explicitly masked to a max of
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* 10 bits, stack-clash style attacks are unlikely. For more details see
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* "VLAs" in Documentation/process/deprecated.rst
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*/
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void *__builtin_alloca(size_t size);
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/*
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* Use, at most, 10 bits of entropy. We explicitly cap this to keep the
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* "VLA" from being unbounded (see above). 10 bits leaves enough room for
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* per-arch offset masks to reduce entropy (by removing higher bits, since
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* high entropy may overly constrain usable stack space), and for
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* compiler/arch-specific stack alignment to remove the lower bits.
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*/
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#define KSTACK_OFFSET_MAX(x) ((x) & 0x3FF)
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/*
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* These macros must be used during syscall entry when interrupts and
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* preempt are disabled, and after user registers have been stored to
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* the stack.
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*/
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#define add_random_kstack_offset() do { \
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if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
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&randomize_kstack_offset)) { \
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u32 offset = raw_cpu_read(kstack_offset); \
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u8 *ptr = __builtin_alloca(KSTACK_OFFSET_MAX(offset)); \
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/* Keep allocation even after "ptr" loses scope. */ \
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asm volatile("" :: "r"(ptr) : "memory"); \
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} \
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} while (0)
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#define choose_random_kstack_offset(rand) do { \
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if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
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&randomize_kstack_offset)) { \
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u32 offset = raw_cpu_read(kstack_offset); \
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offset = ror32(offset, 5) ^ (rand); \
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raw_cpu_write(kstack_offset, offset); \
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} \
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} while (0)
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#else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
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#define add_random_kstack_offset() do { } while (0)
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#define choose_random_kstack_offset(rand) do { } while (0)
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#endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
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#endif
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