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| author |   Kees Cook <keescook@chromium.org> | 2021-04-01 16:23:45 -0700 |
|---|---|---|
| committer |   Thomas Gleixner <tglx@linutronix.de> | 2021-04-08 14:05:20 +0200 |
| commit | fe950f6020338c8ac668ef823bb692d36b7542a2 (patch) | |
| tree | 5bc68b8faf68e62c10d31dd7cc121e4d7fcf8dd2 /arch/x86/include | |
| parent | stack: Optionally randomize kernel stack offset each syscall (diff) | |
| download | linux-dev-fe950f6020338c8ac668ef823bb692d36b7542a2.tar.xz linux-dev-fe950f6020338c8ac668ef823bb692d36b7542a2.zip | |
x86/entry: Enable random_kstack_offset support
Allow for a randomized stack offset on a per-syscall basis, with roughly
5-6 bits of entropy, depending on compiler and word size. Since the
method of offsetting uses macros, this cannot live in the common entry
code (the stack offset needs to be retained for the life of the syscall,
which means it needs to happen at the actual entry point).
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210401232347.2791257-5-keescook@chromium.org
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/entry-common.h | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 2b87b191b3b8..14ebd2196569 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -2,6 +2,7 @@ #ifndef _ASM_X86_ENTRY_COMMON_H #define _ASM_X86_ENTRY_COMMON_H +#include <linux/randomize_kstack.h> #include <linux/user-return-notifier.h> #include <asm/nospec-branch.h> @@ -70,6 +71,21 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, */ current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED); #endif + + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * but not enough for x86 stack utilization comfort. To keep + * reasonable stack head room, reduce the maximum offset to 8 bits. + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints (see cc_stack_align4/8 in + * arch/x86/Makefile), which will remove the 3 (x86_64) or 2 (ia32) + * low bits from any entropy chosen here. + * + * Therefore, final stack offset entropy will be 5 (x86_64) or + * 6 (ia32) bits. + */ + choose_random_kstack_offset(rdtsc() & 0xFF); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare |