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Subject[PATCH v2 16/36] x86/entry/64/compat: Remove most of the fast system call machinery
Date
We now have only one code path that calls through the compat syscall
table. This will make it much more pleasant to change the pt_regs
vs register calling convention, which we need to do to move the call
into C.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/entry/entry_64_compat.S | 246 +--------------------------------------
1 file changed, 4 insertions(+), 242 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 8f847722ce72..3216e6072312 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -101,119 +101,13 @@ sysenter_flags_fixed:
movl $11, %edi
call do_exit

- /*
- * Re-enable interrupts. IRQ tracing already thinks that IRQs are
- * on (since we treat user mode as having IRQs on), and the
- * prologue above is too short for it to be worth adding a
- * tracing round trip.
- */
- ENABLE_INTERRUPTS(CLBR_NONE)
-
- /*
- * no need to do an access_ok check here because rbp has been
- * 32-bit zero extended
- */
- ASM_STAC
-1: movl (%rbp), %ebp
- _ASM_EXTABLE(1b, ia32_badarg)
- ASM_CLAC
-
- orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
- testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
- jnz sysenter_tracesys
-
-sysenter_do_call:
- /* 32-bit syscall -> 64-bit C ABI argument conversion */
- movl %edi, %r8d /* arg5 */
- movl %ebp, %r9d /* arg6 */
- xchg %ecx, %esi /* rsi:arg2, rcx:arg4 */
- movl %ebx, %edi /* arg1 */
- movl %edx, %edx /* arg3 (zero extension) */
-sysenter_dispatch:
- cmpq $(IA32_NR_syscalls-1), %rax
- ja 1f
- call *ia32_sys_call_table(, %rax, 8)
- movq %rax, RAX(%rsp)
-1:
- DISABLE_INTERRUPTS(CLBR_NONE)
- TRACE_IRQS_OFF
- testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
- jnz ia32_ret_from_sys_call_irqs_off
-sysexit_from_sys_call:
- /*
- * NB: SYSEXIT is not obviously safe for 64-bit kernels -- an
- * NMI between STI and SYSEXIT has poorly specified behavior,
- * and and NMI followed by an IRQ with usergs is fatal. So
- * we just pretend we're using SYSEXIT but we really use
- * SYSRETL instead.
- *
- * This code path is still called 'sysexit' because it pairs
- * with 'sysenter' and it uses the SYSENTER calling convention.
- */
- andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
- movl RIP(%rsp), %ecx /* User %eip */
- movq RAX(%rsp), %rax
- movl RSI(%rsp), %esi
- movl RDI(%rsp), %edi
- xorl %edx, %edx /* Do not leak kernel information */
- xorq %r8, %r8
- xorq %r9, %r9
- xorq %r10, %r10
- movl EFLAGS(%rsp), %r11d /* User eflags */
- TRACE_IRQS_ON
-
- /*
- * SYSRETL works even on Intel CPUs. Use it in preference to SYSEXIT,
- * since it avoids a dicey window with interrupts enabled.
- */
- movl RSP(%rsp), %esp
-
- /*
- * USERGS_SYSRET32 does:
- * gsbase = user's gs base
- * eip = ecx
- * rflags = r11
- * cs = __USER32_CS
- * ss = __USER_DS
- *
- * The prologue set RIP(%rsp) to VDSO32_SYSENTER_RETURN, which does:
- *
- * pop %ebp
- * pop %edx
- * pop %ecx
- *
- * Therefore, we invoke SYSRETL with EDX and R8-R10 zeroed to
- * avoid info leaks. R11 ends up with VDSO32_SYSENTER_RETURN's
- * address (already known to user code), and R12-R15 are
- * callee-saved and therefore don't contain any interesting
- * kernel data.
- */
- USERGS_SYSRET32
+ /* Unreachable. */
+ ud2

sysenter_fix_flags:
pushq $X86_EFLAGS_FIXED
popfq
jmp sysenter_flags_fixed
-
-sysenter_tracesys:
- SAVE_EXTRA_REGS
- xorl %eax, %eax /* Do not leak kernel information */
- movq %rax, R11(%rsp)
- movq %rax, R10(%rsp)
- movq %rax, R9(%rsp)
- movq %rax, R8(%rsp)
- movq %rsp, %rdi /* &pt_regs -> arg1 */
- call syscall_trace_enter
-
- /* Reload arg registers from stack. (see sysenter_tracesys) */
- movl RCX(%rsp), %ecx
- movl RDX(%rsp), %edx
- movl RSI(%rsp), %esi
- movl RDI(%rsp), %edi
- movl %eax, %eax /* zero extension */
-
- RESTORE_EXTRA_REGS
- jmp sysenter_do_call
ENDPROC(entry_SYSENTER_compat)

/*
@@ -280,142 +174,10 @@ ENTRY(entry_SYSCALL_compat)
pushq $-ENOSYS /* pt_regs->ax */
sub $(10*8), %rsp /* pt_regs->r8-11, bp, bx, r12-15 not saved */

- /*
- * No need to do an access_ok check here because r8 has been
- * 32-bit zero extended:
- */
- ASM_STAC
-1: movl (%r8), %r9d
- _ASM_EXTABLE(1b, ia32_badarg)
- ASM_CLAC
- orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
- testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
- jnz cstar_tracesys
-
-cstar_do_call:
- /* 32-bit syscall -> 64-bit C ABI argument conversion */
- movl %edi, %r8d /* arg5 */
- /* r9 already loaded */ /* arg6 */
- xchg %ecx, %esi /* rsi:arg2, rcx:arg4 */
- movl %ebx, %edi /* arg1 */
- movl %edx, %edx /* arg3 (zero extension) */
-
-cstar_dispatch:
- cmpq $(IA32_NR_syscalls-1), %rax
- ja 1f
-
- call *ia32_sys_call_table(, %rax, 8)
- movq %rax, RAX(%rsp)
-1:
- DISABLE_INTERRUPTS(CLBR_NONE)
- TRACE_IRQS_OFF
- testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
- jnz ia32_ret_from_sys_call_irqs_off
-
-sysretl_from_sys_call:
- andl $~TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
- movl RDX(%rsp), %edx
- movl RSI(%rsp), %esi
- movl RDI(%rsp), %edi
- movl RIP(%rsp), %ecx
- movl EFLAGS(%rsp), %r11d
- movq RAX(%rsp), %rax
- xorq %r10, %r10
- xorq %r9, %r9
- xorq %r8, %r8
- TRACE_IRQS_ON
- movl RSP(%rsp), %esp
- /*
- * 64-bit->32-bit SYSRET restores eip from ecx,
- * eflags from r11 (but RF and VM bits are forced to 0),
- * cs and ss are loaded from MSRs.
- * (Note: 32-bit->32-bit SYSRET is different: since r11
- * does not exist, it merely sets eflags.IF=1).
- *
- * NB: On AMD CPUs with the X86_BUG_SYSRET_SS_ATTRS bug, the ss
- * descriptor is not reinitialized. This means that we must
- * 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.
- */
- USERGS_SYSRET32
-
-cstar_tracesys:
- xchgl %r9d, %ebp
- SAVE_EXTRA_REGS
- xorl %eax, %eax /* Do not leak kernel information */
- movq %rax, R11(%rsp)
- movq %rax, R10(%rsp)
- movq %r9, R9(%rsp)
- movq %rax, R8(%rsp)
- movq %rsp, %rdi /* &pt_regs -> arg1 */
- call syscall_trace_enter
- movl R9(%rsp), %r9d
-
- /* Reload arg registers from stack. (see sysenter_tracesys) */
- movl RCX(%rsp), %ecx
- movl RDX(%rsp), %edx
- movl RSI(%rsp), %esi
- movl RDI(%rsp), %edi
- movl %eax, %eax /* zero extension */
-
- RESTORE_EXTRA_REGS
- xchgl %ebp, %r9d
- jmp cstar_do_call
+ /* Unreachable. */
+ ud2
END(entry_SYSCALL_compat)

-ia32_badarg:
- /*
- * So far, we've entered kernel mode, set AC, turned on IRQs, and
- * saved C regs except r8-r11. We haven't done any of the other
- * standard entry work, though. We want to bail, but we shouldn't
- * treat this as a syscall entry since we don't even know what the
- * args are. Instead, treat this as a non-syscall entry, finish
- * the entry work, and immediately exit after setting AX = -EFAULT.
- *
- * We're really just being polite here. Killing the task outright
- * would be a reasonable action, too. Given that the only valid
- * way to have gotten here is through the vDSO, and we already know
- * that the stack pointer is bad, the task isn't going to survive
- * for long no matter what we do.
- */
-
- ASM_CLAC /* undo STAC */
- movq $-EFAULT, RAX(%rsp) /* return -EFAULT if possible */
-
- /* Fill in the rest of pt_regs */
- xorl %eax, %eax
- movq %rax, R11(%rsp)
- movq %rax, R10(%rsp)
- movq %rax, R9(%rsp)
- movq %rax, R8(%rsp)
- SAVE_EXTRA_REGS
-
- /* Turn IRQs back off. */
- DISABLE_INTERRUPTS(CLBR_NONE)
- TRACE_IRQS_OFF
-
- /* Now finish entering normal kernel mode. */
-#ifdef CONFIG_CONTEXT_TRACKING
- call enter_from_user_mode
-#endif
-
- /* And exit again. */
- jmp retint_user
-
-ia32_ret_from_sys_call_irqs_off:
- TRACE_IRQS_ON
- ENABLE_INTERRUPTS(CLBR_NONE)
-
-ia32_ret_from_sys_call:
- xorl %eax, %eax /* Do not leak kernel information */
- movq %rax, R11(%rsp)
- movq %rax, R10(%rsp)
- movq %rax, R9(%rsp)
- movq %rax, R8(%rsp)
- jmp int_ret_from_sys_call
-
/*
* Emulated IA32 system calls via int 0x80.
*
--
2.4.3


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