linux-kernel - [tip: x86/entry] x86/entry/32: Provide macro to emit IDT entry stubs

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Date:   Tue, 19 May 2020 19:58:36 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/entry] x86/entry/32: Provide macro to emit IDT entry stubs

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     e94587c501c82a3c9153217a97db11a81ed37f85
Gitweb:        https://git.kernel.org/tip/e94587c501c82a3c9153217a97db11a81ed37f85
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Tue, 25 Feb 2020 23:16:11 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 19 May 2020 16:03:56 +02:00

x86/entry/32: Provide macro to emit IDT entry stubs

32 and 64 bit have unnecessary different ways to populate the exception
entry code. Provide a idtentry macro which allows to consolidate all of
that.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Acked-by: Andy Lutomirski <luto@...nel.org>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20200505134904.166735365@linutronix.de


---
 arch/x86/entry/entry_32.S | 68 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index d9da0b7..eb64e78 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -44,6 +44,7 @@
 #include <asm/asm.h>
 #include <asm/smap.h>
 #include <asm/frame.h>
+#include <asm/trapnr.h>
 #include <asm/nospec-branch.h>
 
 #include "calling.h"
@@ -726,6 +727,31 @@
 
 .Lend_\@:
 .endm
+
+/**
+ * idtentry - Macro to generate entry stubs for simple IDT entries
+ * @vector:		Vector number
+ * @asmsym:		ASM symbol for the entry point
+ * @cfunc:		C function to be called
+ * @has_error_code:	Hardware pushed error code on stack
+ * @sane:		Compatibility flag with 64bit
+ */
+.macro idtentry vector asmsym cfunc has_error_code:req sane=0
+SYM_CODE_START(\asmsym)
+	ASM_CLAC
+	cld
+
+	.if \has_error_code == 0
+		pushl	$0		/* Clear the error code */
+	.endif
+
+	/* Push the C-function address into the GS slot */
+	pushl	$\cfunc
+	/* Invoke the common exception entry */
+	jmp	handle_exception
+SYM_CODE_END(\asmsym)
+.endm
+
 /*
  * %eax: prev task
  * %edx: next task
@@ -1517,6 +1543,48 @@ SYM_CODE_START_LOCAL_NOALIGN(common_exception)
 	jmp	ret_from_exception
 SYM_CODE_END(common_exception)
 
+SYM_CODE_START_LOCAL_NOALIGN(handle_exception)
+	/* the function address is in %gs's slot on the stack */
+	SAVE_ALL switch_stacks=1 skip_gs=1 unwind_espfix=1
+	ENCODE_FRAME_POINTER
+
+	/* fixup %gs */
+	GS_TO_REG %ecx
+	movl	PT_GS(%esp), %edi		# get the function address
+	REG_TO_PTGS %ecx
+	SET_KERNEL_GS %ecx
+
+	/* fixup orig %eax */
+	movl	PT_ORIG_EAX(%esp), %edx		# get the error code
+	movl	$-1, PT_ORIG_EAX(%esp)		# no syscall to restart
+
+	movl	%esp, %eax			# pt_regs pointer
+	CALL_NOSPEC edi
+
+#ifdef CONFIG_VM86
+	movl	PT_EFLAGS(%esp), %eax		# mix EFLAGS and CS
+	movb	PT_CS(%esp), %al
+	andl	$(X86_EFLAGS_VM | SEGMENT_RPL_MASK), %eax
+#else
+	/*
+	 * We can be coming here from child spawned by kernel_thread().
+	 */
+	movl	PT_CS(%esp), %eax
+	andl	$SEGMENT_RPL_MASK, %eax
+#endif
+	cmpl	$USER_RPL, %eax			# returning to v8086 or userspace ?
+	jnb	ret_to_user
+
+	PARANOID_EXIT_TO_KERNEL_MODE
+	BUG_IF_WRONG_CR3
+	RESTORE_REGS 4
+	jmp	.Lirq_return
+
+ret_to_user:
+	movl	%esp, %eax
+	jmp	restore_all_switch_stack
+SYM_CODE_END(handle_exception)
+
 SYM_CODE_START(debug)
 	/*
 	 * Entry from sysenter is now handled in common_exception