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

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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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dominik 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dominik Brodowski 2018-02-14 18:59:23 +01:00 • committed by Ingo Molnar
parent 42ca8082e2
commit 9e809d15d6
2 changed files with 18 additions and 11 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

11
arch/x86/entry/calling.h
View file

@ -97,7 +97,7 @@ For 32-bit we have the following conventions - kernel is built with
#define SIZEOF_PTREGS 21*8 #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 * Push registers and sanitize registers of values that a
* speculation attack might otherwise want to exploit. The * 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. * could be put to use in a speculative execution gadget.
* Interleave XOR with PUSH for better uop scheduling: * 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 %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */ pushq %rsi /* pt_regs->si */
.endif
pushq \rdx /* pt_regs->dx */ pushq \rdx /* pt_regs->dx */
pushq %rcx /* pt_regs->cx */ pushq %rcx /* pt_regs->cx */
pushq \rax /* pt_regs->ax */ 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 */ pushq %r15 /* pt_regs->r15 */
xorq %r15, %r15 /* nospec r15*/ xorq %r15, %r15 /* nospec r15*/
UNWIND_HINT_REGS UNWIND_HINT_REGS
.if \save_ret
pushq %rsi /* return address on top of stack */
.endif
.endm .endm
.macro POP_REGS pop_rdi=1 skip_r11rcx=0 .macro POP_REGS pop_rdi=1 skip_r11rcx=0

18
arch/x86/entry/entry_64.S
View file

@ -875,12 +875,8 @@ ENTRY(\sym)
pushq $-1 /* ORIG_RAX: no syscall to restart */ pushq $-1 /* ORIG_RAX: no syscall to restart */
.endif .endif
/* Save all registers in pt_regs */
PUSH_AND_CLEAR_REGS
ENCODE_FRAME_POINTER
.if \paranoid < 2 .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_\@ jnz .Lfrom_usermode_switch_stack_\@
.endif .endif
@ -1130,13 +1126,15 @@ idtentry machine_check do_mce has_error_code=0 paranoid=1
#endif #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. * Use slow, but surefire "are we in kernel?" check.
* Return: ebx=0: need swapgs on exit, ebx=1: otherwise * Return: ebx=0: need swapgs on exit, ebx=1: otherwise
*/ */
ENTRY(paranoid_entry) ENTRY(paranoid_entry)
UNWIND_HINT_FUNC UNWIND_HINT_FUNC
cld cld
PUSH_AND_CLEAR_REGS save_ret=1
ENCODE_FRAME_POINTER 8
movl $1, %ebx movl $1, %ebx
movl $MSR_GS_BASE, %ecx movl $MSR_GS_BASE, %ecx
rdmsr rdmsr
@ -1181,12 +1179,14 @@ ENTRY(paranoid_exit)
END(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 * Return: EBX=0: came from user mode; EBX=1: otherwise
*/ */
ENTRY(error_entry) ENTRY(error_entry)
UNWIND_HINT_REGS offset=8 UNWIND_HINT_FUNC
cld cld
PUSH_AND_CLEAR_REGS save_ret=1
ENCODE_FRAME_POINTER 8
testb $3, CS+8(%rsp) testb $3, CS+8(%rsp)
jz .Lerror_kernelspace jz .Lerror_kernelspace
@ -1577,8 +1577,6 @@ end_repeat_nmi:
* frame to point back to repeat_nmi. * frame to point back to repeat_nmi.
*/ */
pushq $-1 /* ORIG_RAX: no syscall to restart */ 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 * Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit