Re: [PATCH v3 2/4] x86/syscalls: Specific usage of verify_pre_usermode_state
From: "H. Peter Anvin" <hpa@zytor.com>
Date: 2017-03-14 00:04:36
On 03/11/17 01:42, Ingo Molnar wrote:
quoted
+ /* + * Check user-mode state on fast path return, the same check is done + * under the slow path through syscall_return_slowpath. + */ +#ifdef CONFIG_BUG_ON_DATA_CORRUPTION + call verify_pre_usermode_state +#else + /* + * Similar to set_fs(USER_DS) in verify_pre_usermode_state without a + * warning. + */ + movq PER_CPU_VAR(current_task), %rax + movq $TASK_SIZE_MAX, %rcx + cmp %rcx, TASK_addr_limit(%rax) + jz 1f + movq %rcx, TASK_addr_limit(%rax) +1: +#endif +
How about simply doing... movq PER_CPU_VAR(current_task), %rax movq $TASK_SIZE_MAX, %rcx #ifdef CONFIG_BUG_ON_DATA_CORRUPTION cmpq %rcx, TASK_addr_limit(%rax) jne syscall_return_slowpath #else movq %rcx, TASK_addr_limit(%rax) #endif ... and let the slow path take care of BUG. This should be much faster, even with the BUG, and is simpler to boot. -hpa