Commit ee774dac authored Apr 21, 2022 by Lai Jiangshan Committed by Borislav Petkov May 03, 2022

x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()



The macro idtentry() (through idtentry_body()) calls error_entry()
unconditionally even on XENPV. But XENPV needs to only push and clear
regs.

PUSH_AND_CLEAR_REGS in error_entry() makes the stack not return to its
original place when the function returns, which means it is not possible
to convert it to a C function.

Carve out PUSH_AND_CLEAR_REGS out of error_entry() and into a separate
function and call it before error_entry() in order to avoid calling
error_entry() on XENPV.

It will also allow for error_entry() to be converted to C code that can
use inlined sync_regs() and save a function call.

  [ bp: Massage commit message. ]

Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20220503032107.680190-4-jiangshanlai@gmail.com

parent 520a7e80

arch/x86/entry/entry_64.S

+12 −3

Original line number	Diff line number	Diff line
		@@ -318,6 +318,14 @@ SYM_CODE_END(ret_from_fork)
		#endif
		.endm

		/* Save all registers in pt_regs */
		SYM_CODE_START_LOCAL(push_and_clear_regs)
		UNWIND_HINT_FUNC
		PUSH_AND_CLEAR_REGS save_ret=1
		ENCODE_FRAME_POINTER 8
		RET
		SYM_CODE_END(push_and_clear_regs)

		/**
		* idtentry_body - Macro to emit code calling the C function
		* @cfunc: C function to be called
		@@ -325,6 +333,9 @@ SYM_CODE_END(ret_from_fork)
		*/
		.macro idtentry_body cfunc has_error_code:req

		call push_and_clear_regs
		UNWIND_HINT_REGS

		call error_entry
		movq %rax, %rsp /* switch to the task stack if from userspace */
		ENCODE_FRAME_POINTER
		@@ -985,13 +996,11 @@ SYM_CODE_START_LOCAL(paranoid_exit)
		SYM_CODE_END(paranoid_exit)

		/*
		* Save all registers in pt_regs, and switch GS if needed.
		* Switch GS and CR3 if needed.
		*/
		SYM_CODE_START_LOCAL(error_entry)
		UNWIND_HINT_FUNC
		cld
		PUSH_AND_CLEAR_REGS save_ret=1
		ENCODE_FRAME_POINTER 8
		testb $3, CS+8(%rsp)
		jz .Lerror_kernelspace