diff options
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/arm64/kernel/syscall.c | 16 | ||||
| -rw-r--r-- | arch/s390/include/asm/entry-common.h | 2 | ||||
| -rw-r--r-- | arch/x86/include/asm/entry-common.h | 15 |
3 files changed, 14 insertions, 19 deletions
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index ad198262b981..7230f6e20ab8 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -53,17 +53,15 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno, syscall_set_return_value(current, regs, 0, ret); /* - * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), - * but not enough for arm64 stack utilization comfort. To keep - * reasonable stack head room, reduce the maximum offset to 9 bits. + * This value will get limited by KSTACK_OFFSET_MAX(), which is 10 + * bits. The actual entropy will be further reduced by the compiler + * when applying stack alignment constraints: the AAPCS mandates a + * 16-byte aligned SP at function boundaries, which will remove the + * 4 low bits from any entropy chosen here. * - * The actual entropy will be further reduced by the compiler when - * applying stack alignment constraints: the AAPCS mandates a - * 16-byte (i.e. 4-bit) aligned SP at function boundaries. - * - * The resulting 5 bits of entropy is seen in SP[8:4]. + * The resulting 6 bits of entropy is seen in SP[9:4]. */ - choose_random_kstack_offset(get_random_u16() & 0x1FF); + choose_random_kstack_offset(get_random_u16()); } static inline bool has_syscall_work(unsigned long flags) diff --git a/arch/s390/include/asm/entry-common.h b/arch/s390/include/asm/entry-common.h index 7f5004065e8a..35555c944630 100644 --- a/arch/s390/include/asm/entry-common.h +++ b/arch/s390/include/asm/entry-common.h @@ -54,7 +54,7 @@ static __always_inline void arch_exit_to_user_mode(void) static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, unsigned long ti_work) { - choose_random_kstack_offset(get_tod_clock_fast() & 0xff); + choose_random_kstack_offset(get_tod_clock_fast()); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h index 7e523bb3d2d3..fb2809b20b0a 100644 --- a/arch/x86/include/asm/entry-common.h +++ b/arch/x86/include/asm/entry-common.h @@ -73,19 +73,16 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, #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 + * This value will get limited by KSTACK_OFFSET_MAX(), which is 10 + * 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. + * Therefore, final stack offset entropy will be 7 (x86_64) or + * 8 (ia32) bits. */ - choose_random_kstack_offset(rdtsc() & 0xFF); + choose_random_kstack_offset(rdtsc()); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare |