[PATCH V4 4/6] x86/entry/32: Restore %fs before switching stack

From: Lai Jiangshan <jiangshanlai@gmail.com>
To: linux-kernel@vger.kernel.org, Borislav Petkov <bp@alien8.de>
Cc: Lai Jiangshan <laijs@linux.alibaba.com>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Joerg Roedel <jroedel@suse.de>,
	Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	Balbir Singh <sblbir@amazon.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Gabriel Krisman Bertazi <krisman@collabora.com>,
	Kees Cook <keescook@chromium.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Jens Axboe <axboe@kernel.dk>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Brian Gerst <brgerst@gmail.com>, Ard Biesheuvel <ardb@kernel.org>,
	Andi Kleen <ak@linux.intel.com>, Mike Rapoport <rppt@kernel.org>,
	Mike Hommey <mh@glandium.org>,
	Mark Gross <mgross@linux.intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Anthony Steinhauser <asteinhauser@google.com>,
	Jay Lang <jaytlang@mit.edu>,
	"Chang S. Bae" <chang.seok.bae@intel.com>
Subject: [PATCH V4 4/6] x86/entry/32: Restore %fs before switching stack
Date: Wed, 10 Feb 2021 21:39:15 +0800	[thread overview]
Message-ID: <20210210133917.2414-5-jiangshanlai@gmail.com> (raw)
In-Reply-To: <20210210133917.2414-1-jiangshanlai@gmail.com>

From: Lai Jiangshan <laijs@linux.alibaba.com>

entry_SYSENTER_32 saves the user %fs in the entry stack and restores the
kernel %fs before loading the task stack for stack switching, so that it
can use percpu before switching stack in the next patch.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
 arch/x86/entry/entry_32.S | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3e693db0963d..01f098c5b017 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -279,11 +279,13 @@
 .Lfinished_frame_\@:
 .endm
 
-.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0 skip_gs=0 unwind_espfix=0
+.macro SAVE_ALL pt_regs_ax=%eax switch_stacks=0 skip_gs=0 skip_fs=0 unwind_espfix=0
 	cld
 .if \skip_gs == 0
 	PUSH_GS
 .endif
+
+.if \skip_fs == 0
 	pushl	%fs
 
 	pushl	%eax
@@ -293,6 +295,7 @@
 	UNWIND_ESPFIX_STACK
 .endif
 	popl	%eax
+.endif
 
 	FIXUP_FRAME
 	pushl	%es
@@ -906,18 +909,27 @@ SYM_FUNC_START(entry_SYSENTER_32)
 	BUG_IF_WRONG_CR3 no_user_check=1
 	SWITCH_TO_KERNEL_CR3 scratch_reg=%eax
 
+	/* Restore kernel %fs, so that we can use PERCPU */
+	pushl	%fs
+	movl	$(__KERNEL_PERCPU), %eax
+	movl	%eax, %fs
+
 	/* Switch to task stack */
 	movl	%esp, %eax
-	movl	(2*4+TSS_entry2task_stack)(%esp), %esp
+	movl	(3*4+TSS_entry2task_stack)(%esp), %esp
 
 .Lsysenter_past_esp:
 	pushl	$__USER_DS		/* pt_regs->ss */
 	pushl	$0			/* pt_regs->sp (placeholder) */
-	pushl	%ss:4(%eax)		/* pt_regs->flags (except IF = 0) */
+	pushl	%ss:8(%eax)		/* pt_regs->flags (except IF = 0) */
 	pushl	$__USER_CS		/* pt_regs->cs */
 	pushl	$0			/* pt_regs->ip = 0 (placeholder) */
-	pushl	%ss:(%eax)		/* pt_regs->orig_ax */
-	SAVE_ALL pt_regs_ax=$-ENOSYS	/* save rest, stack already switched */
+	pushl	%ss:4(%eax)		/* pt_regs->orig_ax */
+	PUSH_GS				/* pt_regs->gs */
+	pushl	%ss:(%eax)		/* pt_regs->fs */
+	/* save rest, stack and %fs already switched */
+	SAVE_ALL pt_regs_ax=$-ENOSYS skip_gs=1 skip_fs=1
+	SET_KERNEL_GS %edx
 
 	/*
 	 * SYSENTER doesn't filter flags, so we need to clear NT, AC
-- 
2.19.1.6.gb485710b

