diff options
| -rw-r--r-- | arch/x86/entry/entry_64.S | 39 |
1 files changed, 31 insertions, 8 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index bd97161..3bb2c43 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1135,7 +1135,7 @@ END(paranoid_exit) /* * Save all registers in pt_regs, and switch gs if needed. - * Return: ebx=0: need swapgs on exit, ebx=1: otherwise + * Return: EBX=0: came from user mode; EBX=1: otherwise */ ENTRY(error_entry) cld @@ -1144,9 +1144,11 @@ ENTRY(error_entry) xorl %ebx, %ebx testb $3, CS+8(%rsp) jz error_kernelspace -error_swapgs: + + /* We entered from user mode */ SWAPGS -error_sti: + +error_entry_done: TRACE_IRQS_OFF ret @@ -1165,8 +1167,15 @@ error_kernelspace: cmpq %rax, RIP+8(%rsp) je bstep_iret cmpq $gs_change, RIP+8(%rsp) - je error_swapgs - jmp error_sti + jne error_entry_done + + /* + * hack: gs_change can fail with user gsbase. If this happens, fix up + * gsbase and proceed. We'll fix up the exception and land in + * gs_change's error handler with kernel gsbase. + */ + SWAPGS + jmp error_entry_done bstep_iret: /* Fix truncated RIP */ @@ -1174,16 +1183,30 @@ bstep_iret: /* fall through */ error_bad_iret: + /* + * We came from an IRET to user mode, so we have user gsbase. + * Switch to kernel gsbase: + */ SWAPGS + + /* + * Pretend that the exception came from user mode: set up pt_regs + * as if we faulted immediately after IRET and clear EBX so that + * error_exit knows that we will be returning to user mode. + */ mov %rsp, %rdi call fixup_bad_iret mov %rax, %rsp - decl %ebx /* Return to usergs */ - jmp error_sti + decl %ebx + jmp error_entry_done END(error_entry) -/* On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it) */ +/* + * On entry, EBS is a "return to kernel mode" flag: + * 1: already in kernel mode, don't need SWAPGS + * 0: user gsbase is loaded, we need SWAPGS and standard preparation for return to usermode + */ ENTRY(error_exit) movl %ebx, %eax RESTORE_EXTRA_REGS |