diff options
Diffstat (limited to 'arch/x86/entry/entry_64.S')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 286 |
1 files changed, 110 insertions, 176 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 9d34d3cfceb6..858b555e274b 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -103,6 +103,16 @@ ENDPROC(native_usergs_sysret64) /* * 64-bit SYSCALL instruction entry. Up to 6 arguments in registers. * + * This is the only entry point used for 64-bit system calls. The + * hardware interface is reasonably well designed and the register to + * argument mapping Linux uses fits well with the registers that are + * available when SYSCALL is used. + * + * SYSCALL instructions can be found inlined in libc implementations as + * well as some other programs and libraries. There are also a handful + * of SYSCALL instructions in the vDSO used, for example, as a + * clock_gettimeofday fallback. + * * 64-bit SYSCALL saves rip to rcx, clears rflags.RF, then saves rflags to r11, * then loads new ss, cs, and rip from previously programmed MSRs. * rflags gets masked by a value from another MSR (so CLD and CLAC @@ -145,17 +155,11 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) movq %rsp, PER_CPU_VAR(rsp_scratch) movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp + TRACE_IRQS_OFF + /* Construct struct pt_regs on stack */ pushq $__USER_DS /* pt_regs->ss */ pushq PER_CPU_VAR(rsp_scratch) /* pt_regs->sp */ - /* - * Re-enable interrupts. - * We use 'rsp_scratch' as a scratch space, hence irq-off block above - * must execute atomically in the face of possible interrupt-driven - * task preemption. We must enable interrupts only after we're done - * with using rsp_scratch: - */ - ENABLE_INTERRUPTS(CLBR_NONE) pushq %r11 /* pt_regs->flags */ pushq $__USER_CS /* pt_regs->cs */ pushq %rcx /* pt_regs->ip */ @@ -171,9 +175,21 @@ GLOBAL(entry_SYSCALL_64_after_swapgs) pushq %r11 /* pt_regs->r11 */ sub $(6*8), %rsp /* pt_regs->bp, bx, r12-15 not saved */ - testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) - jnz tracesys + /* + * If we need to do entry work or if we guess we'll need to do + * exit work, go straight to the slow path. + */ + testl $_TIF_WORK_SYSCALL_ENTRY|_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) + jnz entry_SYSCALL64_slow_path + entry_SYSCALL_64_fastpath: + /* + * Easy case: enable interrupts and issue the syscall. If the syscall + * needs pt_regs, we'll call a stub that disables interrupts again + * and jumps to the slow path. + */ + TRACE_IRQS_ON + ENABLE_INTERRUPTS(CLBR_NONE) #if __SYSCALL_MASK == ~0 cmpq $__NR_syscall_max, %rax #else @@ -182,103 +198,56 @@ entry_SYSCALL_64_fastpath: #endif ja 1f /* return -ENOSYS (already in pt_regs->ax) */ movq %r10, %rcx + + /* + * This call instruction is handled specially in stub_ptregs_64. + * It might end up jumping to the slow path. If it jumps, RAX + * and all argument registers are clobbered. + */ call *sys_call_table(, %rax, 8) +.Lentry_SYSCALL_64_after_fastpath_call: + movq %rax, RAX(%rsp) 1: -/* - * Syscall return path ending with SYSRET (fast path). - * Has incompletely filled pt_regs. - */ - LOCKDEP_SYS_EXIT - /* - * We do not frame this tiny irq-off block with TRACE_IRQS_OFF/ON, - * it is too small to ever cause noticeable irq latency. - */ - DISABLE_INTERRUPTS(CLBR_NONE) /* - * We must check ti flags with interrupts (or at least preemption) - * off because we must *never* return to userspace without - * processing exit work that is enqueued if we're preempted here. - * In particular, returning to userspace with any of the one-shot - * flags (TIF_NOTIFY_RESUME, TIF_USER_RETURN_NOTIFY, etc) set is - * very bad. + * If we get here, then we know that pt_regs is clean for SYSRET64. + * If we see that no exit work is required (which we are required + * to check with IRQs off), then we can go straight to SYSRET64. */ + DISABLE_INTERRUPTS(CLBR_NONE) + TRACE_IRQS_OFF testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS) - jnz int_ret_from_sys_call_irqs_off /* Go to the slow path */ + jnz 1f - RESTORE_C_REGS_EXCEPT_RCX_R11 + LOCKDEP_SYS_EXIT + TRACE_IRQS_ON /* user mode is traced as IRQs on */ movq RIP(%rsp), %rcx movq EFLAGS(%rsp), %r11 + RESTORE_C_REGS_EXCEPT_RCX_R11 movq RSP(%rsp), %rsp - /* - * 64-bit SYSRET restores rip from rcx, - * rflags from r11 (but RF and VM bits are forced to 0), - * cs and ss are loaded from MSRs. - * Restoration of rflags re-enables interrupts. - * - * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss - * descriptor is not reinitialized. This means that we should - * avoid SYSRET with SS == NULL, which could happen if we schedule, - * exit the kernel, and re-enter using an interrupt vector. (All - * interrupt entries on x86_64 set SS to NULL.) We prevent that - * from happening by reloading SS in __switch_to. (Actually - * detecting the failure in 64-bit userspace is tricky but can be - * done.) - */ USERGS_SYSRET64 -GLOBAL(int_ret_from_sys_call_irqs_off) +1: + /* + * The fast path looked good when we started, but something changed + * along the way and we need to switch to the slow path. Calling + * raise(3) will trigger this, for example. IRQs are off. + */ TRACE_IRQS_ON ENABLE_INTERRUPTS(CLBR_NONE) - jmp int_ret_from_sys_call - - /* Do syscall entry tracing */ -tracesys: - movq %rsp, %rdi - movl $AUDIT_ARCH_X86_64, %esi - call syscall_trace_enter_phase1 - test %rax, %rax - jnz tracesys_phase2 /* if needed, run the slow path */ - RESTORE_C_REGS_EXCEPT_RAX /* else restore clobbered regs */ - movq ORIG_RAX(%rsp), %rax - jmp entry_SYSCALL_64_fastpath /* and return to the fast path */ - -tracesys_phase2: SAVE_EXTRA_REGS movq %rsp, %rdi - movl $AUDIT_ARCH_X86_64, %esi - movq %rax, %rdx - call syscall_trace_enter_phase2 - - /* - * Reload registers from stack in case ptrace changed them. - * We don't reload %rax because syscall_trace_entry_phase2() returned - * the value it wants us to use in the table lookup. - */ - RESTORE_C_REGS_EXCEPT_RAX - RESTORE_EXTRA_REGS -#if __SYSCALL_MASK == ~0 - cmpq $__NR_syscall_max, %rax -#else - andl $__SYSCALL_MASK, %eax - cmpl $__NR_syscall_max, %eax -#endif - ja 1f /* return -ENOSYS (already in pt_regs->ax) */ - movq %r10, %rcx /* fixup for C */ - call *sys_call_table(, %rax, 8) - movq %rax, RAX(%rsp) -1: - /* Use IRET because user could have changed pt_regs->foo */ + call syscall_return_slowpath /* returns with IRQs disabled */ + jmp return_from_SYSCALL_64 -/* - * Syscall return path ending with IRET. - * Has correct iret frame. - */ -GLOBAL(int_ret_from_sys_call) +entry_SYSCALL64_slow_path: + /* IRQs are off. */ SAVE_EXTRA_REGS movq %rsp, %rdi - call syscall_return_slowpath /* returns with IRQs disabled */ + call do_syscall_64 /* returns with IRQs disabled */ + +return_from_SYSCALL_64: RESTORE_EXTRA_REGS TRACE_IRQS_IRETQ /* we're about to change IF */ @@ -355,83 +324,45 @@ opportunistic_sysret_failed: jmp restore_c_regs_and_iret END(entry_SYSCALL_64) +ENTRY(stub_ptregs_64) + /* + * Syscalls marked as needing ptregs land here. + * If we are on the fast path, we need to save the extra regs, + * which we achieve by trying again on the slow path. If we are on + * the slow path, the extra regs are already saved. + * + * RAX stores a pointer to the C function implementing the syscall. + * IRQs are on. + */ + cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp) + jne 1f - .macro FORK_LIKE func -ENTRY(stub_\func) - SAVE_EXTRA_REGS 8 - jmp sys_\func -END(stub_\func) - .endm - - FORK_LIKE clone - FORK_LIKE fork - FORK_LIKE vfork - -ENTRY(stub_execve) - call sys_execve -return_from_execve: - testl %eax, %eax - jz 1f - /* exec failed, can use fast SYSRET code path in this case */ - ret -1: - /* must use IRET code path (pt_regs->cs may have changed) */ - addq $8, %rsp - ZERO_EXTRA_REGS - movq %rax, RAX(%rsp) - jmp int_ret_from_sys_call -END(stub_execve) -/* - * Remaining execve stubs are only 7 bytes long. - * ENTRY() often aligns to 16 bytes, which in this case has no benefits. - */ - .align 8 -GLOBAL(stub_execveat) - call sys_execveat - jmp return_from_execve -END(stub_execveat) - -#if defined(CONFIG_X86_X32_ABI) - .align 8 -GLOBAL(stub_x32_execve) - call compat_sys_execve - jmp return_from_execve -END(stub_x32_execve) - .align 8 -GLOBAL(stub_x32_execveat) - call compat_sys_execveat - jmp return_from_execve -END(stub_x32_execveat) -#endif - -/* - * sigreturn is special because it needs to restore all registers on return. - * This cannot be done with SYSRET, so use the IRET return path instead. - */ -ENTRY(stub_rt_sigreturn) /* - * SAVE_EXTRA_REGS result is not normally needed: - * sigreturn overwrites all pt_regs->GPREGS. - * But sigreturn can fail (!), and there is no easy way to detect that. - * To make sure RESTORE_EXTRA_REGS doesn't restore garbage on error, - * we SAVE_EXTRA_REGS here. + * Called from fast path -- disable IRQs again, pop return address + * and jump to slow path */ - SAVE_EXTRA_REGS 8 - call sys_rt_sigreturn -return_from_stub: - addq $8, %rsp - RESTORE_EXTRA_REGS - movq %rax, RAX(%rsp) - jmp int_ret_from_sys_call -END(stub_rt_sigreturn) + DISABLE_INTERRUPTS(CLBR_NONE) + TRACE_IRQS_OFF + popq %rax + jmp entry_SYSCALL64_slow_path -#ifdef CONFIG_X86_X32_ABI -ENTRY(stub_x32_rt_sigreturn) - SAVE_EXTRA_REGS 8 - call sys32_x32_rt_sigreturn - jmp return_from_stub -END(stub_x32_rt_sigreturn) -#endif +1: + /* Called from C */ + jmp *%rax /* called from C */ +END(stub_ptregs_64) + +.macro ptregs_stub func +ENTRY(ptregs_\func) + leaq \func(%rip), %rax + jmp stub_ptregs_64 +END(ptregs_\func) +.endm + +/* Instantiate ptregs_stub for each ptregs-using syscall */ +#define __SYSCALL_64_QUAL_(sym) +#define __SYSCALL_64_QUAL_ptregs(sym) ptregs_stub sym +#define __SYSCALL_64(nr, sym, qual) __SYSCALL_64_QUAL_##qual(sym) +#include <asm/syscalls_64.h> /* * A newly forked process directly context switches into this address. @@ -439,7 +370,6 @@ END(stub_x32_rt_sigreturn) * rdi: prev task we switched from */ ENTRY(ret_from_fork) - LOCK ; btr $TIF_FORK, TI_flags(%r8) pushq $0x0002 @@ -447,28 +377,32 @@ ENTRY(ret_from_fork) call schedule_tail /* rdi: 'prev' task parameter */ - RESTORE_EXTRA_REGS - testb $3, CS(%rsp) /* from kernel_thread? */ + jnz 1f /* - * By the time we get here, we have no idea whether our pt_regs, - * ti flags, and ti status came from the 64-bit SYSCALL fast path, - * the slow path, or one of the 32-bit compat paths. - * Use IRET code path to return, since it can safely handle - * all of the above. + * We came from kernel_thread. This code path is quite twisted, and + * someone should clean it up. + * + * copy_thread_tls stashes the function pointer in RBX and the + * parameter to be passed in RBP. The called function is permitted + * to call do_execve and thereby jump to user mode. */ - jnz int_ret_from_sys_call + movq RBP(%rsp), %rdi + call *RBX(%rsp) + movl $0, RAX(%rsp) /* - * We came from kernel_thread - * nb: we depend on RESTORE_EXTRA_REGS above + * Fall through as though we're exiting a syscall. This makes a + * twisted sort of sense if we just called do_execve. */ - movq %rbp, %rdi - call *%rbx - movl $0, RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + +1: + movq %rsp, %rdi + call syscall_return_slowpath /* returns with IRQs disabled */ + TRACE_IRQS_ON /* user mode is traced as IRQS on */ + SWAPGS + jmp restore_regs_and_iret END(ret_from_fork) /* |