[RFC 14/30] x86/entry/64/compat: Remove most of the fast system call machinery

[Andy Lutomirski]

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@xxxxxxxxxx>
---
 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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