Commit 9e809d15 authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Ingo Molnar
Browse files

x86/entry: Reduce the code footprint of the 'idtentry' macro 



Play a little trick in the generic PUSH_AND_CLEAR_REGS macro
to insert the GP registers "above" the original return address.

This allows us to (re-)insert the macro in error_entry() and
paranoid_entry() and to remove it from the idtentry macro. This
reduces the static footprint significantly:

   text	   data	    bss	    dec	    hex	filename
  24307	      0	      0	  24307	   5ef3	entry_64.o-orig
  20987	      0	      0	  20987	   51fb	entry_64.o

Co-developed-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180214175924.23065-2-linux@dominikbrodowski.net


[ Small tweaks to comments. ]
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 42ca8082

arch/x86/entry/calling.h

+10 −1
Original line number Diff line number Diff line
@@ -97,7 +97,7 @@ For 32-bit we have the following conventions - kernel is built with 


#define SIZEOF_PTREGS	21*8



.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax

.macro PUSH_AND_CLEAR_REGS rdx=%rdx rax=%rax save_ret=0

	/*

	 * Push registers and sanitize registers of values that a

	 * speculation attack might otherwise want to exploit. The
@@ -105,8 +105,14 @@ For 32-bit we have the following conventions - kernel is built with 
	 * could be put to use in a speculative execution gadget.

	 * Interleave XOR with PUSH for better uop scheduling:

	 */

	.if \save_ret

	pushq	%rsi		/* pt_regs->si */

	movq	8(%rsp), %rsi	/* temporarily store the return address in %rsi */

	movq	%rdi, 8(%rsp)	/* pt_regs->di (overwriting original return address) */

	.else

	pushq   %rdi		/* pt_regs->di */

	pushq   %rsi		/* pt_regs->si */

	.endif

	pushq	\rdx		/* pt_regs->dx */

	pushq   %rcx		/* pt_regs->cx */

	pushq   \rax		/* pt_regs->ax */
@@ -131,6 +137,9 @@ For 32-bit we have the following conventions - kernel is built with 
	pushq	%r15		/* pt_regs->r15 */

	xorq    %r15, %r15	/* nospec   r15*/

	UNWIND_HINT_REGS

	.if \save_ret

	pushq	%rsi		/* return address on top of stack */

	.endif

.endm



.macro POP_REGS pop_rdi=1 skip_r11rcx=0

arch/x86/entry/entry_64.S

+8 −10
Original line number Diff line number Diff line
@@ -875,12 +875,8 @@ ENTRY(\sym) 
	pushq	$-1				/* ORIG_RAX: no syscall to restart */

	.endif



	/* Save all registers in pt_regs */

	PUSH_AND_CLEAR_REGS

	ENCODE_FRAME_POINTER



	.if \paranoid < 2

	testb	$3, CS(%rsp)			/* If coming from userspace, switch stacks */

	testb	$3, CS-ORIG_RAX(%rsp)		/* If coming from userspace, switch stacks */

	jnz	.Lfrom_usermode_switch_stack_\@

	.endif
@@ -1130,13 +1126,15 @@ idtentry machine_check do_mce has_error_code=0 paranoid=1 
#endif



/*

 * Switch gs if needed.

 * Save all registers in pt_regs, and switch gs if needed.

 * Use slow, but surefire "are we in kernel?" check.

 * Return: ebx=0: need swapgs on exit, ebx=1: otherwise

 */

ENTRY(paranoid_entry)

	UNWIND_HINT_FUNC

	cld

	PUSH_AND_CLEAR_REGS save_ret=1

	ENCODE_FRAME_POINTER 8

	movl	$1, %ebx

	movl	$MSR_GS_BASE, %ecx

	rdmsr
@@ -1181,12 +1179,14 @@ ENTRY(paranoid_exit) 
END(paranoid_exit)



/*

 * Switch gs if needed.

 * Save all registers in pt_regs, and switch GS if needed.

 * Return: EBX=0: came from user mode; EBX=1: otherwise

 */

ENTRY(error_entry)

	UNWIND_HINT_REGS offset=8

	UNWIND_HINT_FUNC

	cld

	PUSH_AND_CLEAR_REGS save_ret=1

	ENCODE_FRAME_POINTER 8

	testb	$3, CS+8(%rsp)

	jz	.Lerror_kernelspace
@@ -1577,8 +1577,6 @@ end_repeat_nmi: 
	 * frame to point back to repeat_nmi.

	 */

	pushq	$-1				/* ORIG_RAX: no syscall to restart */

	PUSH_AND_CLEAR_REGS

	ENCODE_FRAME_POINTER



	/*

	 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit

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