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Commit ef593260 authored by Denys Vlasenko's avatar Denys Vlasenko Committed by Ingo Molnar
Browse files

x86/asm/entry: Get rid of KERNEL_STACK_OFFSET 



PER_CPU_VAR(kernel_stack) was set up in a way where it points
five stack slots below the top of stack.

Presumably, it was done to avoid one "sub $5*8,%rsp"
in syscall/sysenter code paths, where iret frame needs to be
created by hand.

Ironically, none of them benefits from this optimization,
since all of them need to allocate additional data on stack
(struct pt_regs), so they still have to perform subtraction.

This patch eliminates KERNEL_STACK_OFFSET.

PER_CPU_VAR(kernel_stack) now points directly to top of stack.
pt_regs allocations are adjusted to allocate iret frame as well.
Hopefully we can merge it later with 32-bit specific
PER_CPU_VAR(cpu_current_top_of_stack) variable...

Net result in generated code is that constants in several insns
are changed.

This change is necessary for changing struct pt_regs creation
in SYSCALL64 code path from MOV to PUSH instructions.

Signed-off-by: default avatarDenys Vlasenko <dvlasenk@redhat.com>
Acked-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1426785469-15125-2-git-send-email-dvlasenk@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent b3fe8ba3

arch/x86/ia32/ia32entry.S

+2 −2
Original line number Diff line number Diff line
@@ -311,7 +311,7 @@ ENDPROC(ia32_sysenter_target) 
ENTRY(ia32_cstar_target)

	CFI_STARTPROC32	simple

	CFI_SIGNAL_FRAME

	CFI_DEF_CFA	rsp,KERNEL_STACK_OFFSET

	CFI_DEF_CFA	rsp,0

	CFI_REGISTER	rip,rcx

	/*CFI_REGISTER	rflags,r11*/

	SWAPGS_UNSAFE_STACK
@@ -323,7 +323,7 @@ ENTRY(ia32_cstar_target) 
	 * disabled irqs and here we enable it straight after entry:

	 */

	ENABLE_INTERRUPTS(CLBR_NONE)

	ALLOC_PT_GPREGS_ON_STACK 8	/* +8: space for orig_ax */

	ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */

	SAVE_C_REGS_EXCEPT_RCX_R891011

	movl 	%eax,%eax	/* zero extension */

	movq	%rax,ORIG_RAX(%rsp)

arch/x86/include/asm/thread_info.h

+2 −3
Original line number Diff line number Diff line
@@ -172,7 +172,6 @@ struct thread_info { 
#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)



#define STACK_WARN		(THREAD_SIZE/8)

#define KERNEL_STACK_OFFSET	(5*(BITS_PER_LONG/8))



/*

 * macros/functions for gaining access to the thread information structure
@@ -201,10 +200,10 @@ static inline unsigned long current_stack_pointer(void) 


#else /* !__ASSEMBLY__ */



/* how to get the thread information struct from ASM */

/* Load thread_info address into "reg" */

#define GET_THREAD_INFO(reg) \

	_ASM_MOV PER_CPU_VAR(kernel_stack),reg ; \

	_ASM_SUB $(THREAD_SIZE-KERNEL_STACK_OFFSET),reg ;

	_ASM_SUB $(THREAD_SIZE),reg ;



/*

 * ASM operand which evaluates to thread_info address

arch/x86/kernel/cpu/common.c

+1 −1
Original line number Diff line number Diff line
@@ -1116,7 +1116,7 @@ static __init int setup_disablecpuid(char *arg) 
__setup("clearcpuid=", setup_disablecpuid);



DEFINE_PER_CPU(unsigned long, kernel_stack) =

	(unsigned long)&init_thread_union - KERNEL_STACK_OFFSET + THREAD_SIZE;

	(unsigned long)&init_thread_union + THREAD_SIZE;

EXPORT_PER_CPU_SYMBOL(kernel_stack);



#ifdef CONFIG_X86_64

arch/x86/kernel/entry_64.S

+2 −3
Original line number Diff line number Diff line
@@ -225,7 +225,7 @@ ENDPROC(native_usergs_sysret64) 
ENTRY(system_call)

	CFI_STARTPROC	simple

	CFI_SIGNAL_FRAME

	CFI_DEF_CFA	rsp,KERNEL_STACK_OFFSET

	CFI_DEF_CFA	rsp,0

	CFI_REGISTER	rip,rcx

	/*CFI_REGISTER	rflags,r11*/

	SWAPGS_UNSAFE_STACK
@@ -242,9 +242,8 @@ GLOBAL(system_call_after_swapgs) 
	 * so we can enable interrupts only after we're done with using rsp_scratch:

	 */

	movq	%rsp,PER_CPU_VAR(rsp_scratch)

	/* kernel_stack is set so that 5 slots (iret frame) are preallocated */

	movq	PER_CPU_VAR(kernel_stack),%rsp

	ALLOC_PT_GPREGS_ON_STACK 8		/* +8: space for orig_ax */

	ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */

	movq	%rcx,RIP(%rsp)

	movq	PER_CPU_VAR(rsp_scratch),%rcx

	movq	%r11,EFLAGS(%rsp)

arch/x86/kernel/process_32.c

+1 −1
Original line number Diff line number Diff line
@@ -308,7 +308,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	load_sp0(tss, next);

	this_cpu_write(kernel_stack,

		       (unsigned long)task_stack_page(next_p) +

		       THREAD_SIZE - KERNEL_STACK_OFFSET);

		       THREAD_SIZE);

	this_cpu_write(cpu_current_top_of_stack,

		       (unsigned long)task_stack_page(next_p) +

		       THREAD_SIZE);