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x86/asm/entry/64: Clean up and document various entry code details 

This patch does a lot of cleanup in comments and formatting,
but it does not change any code:

 - Rename 'save_paranoid' to 'paranoid_entry': this makes naming
   similar to its "non-paranoid" sibling, 'error_entry',
   and to its counterpart, 'paranoid_exit'.

 - Use the same CFI annotation atop 'paranoid_entry' and 'error_entry'.

 - Fix irregular indentation of assembler operands.

 - Add/fix comments on top of 'paranoid_entry' and 'error_entry'.

 - Remove stale comment about "oldrax".

 - Make comments about "no swapgs" flag in ebx more prominent.

 - Deindent wrongly indented top-level comment atop 'paranoid_exit'.

 - Indent wrongly deindented comment inside 'error_entry'.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Alexei Starovoitov <ast@plumgrid.com>
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: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/4640f9fcd5ea46eb299b1cd6d3f5da3167d2f78d.1424989793.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Denys Vlasenko 2015-02-26 14:40:34 -08:00 committed by Ingo Molnar
parent 1eeb207f87
commit ebfc453e27
1 changed files with 36 additions and 32 deletions
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68
arch/x86/kernel/entry_64.S
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@ -982,10 +982,11 @@ ENTRY(\sym)
testl $3, CS(%rsp) /* If coming from userspace, switch */
jnz 1f /* stacks. */
.endif
call save_paranoid
call paranoid_entry
.else
call error_entry
.endif
/* returned flag: ebx=0: need swapgs on exit, ebx=1: don't need it */
DEFAULT_FRAME 0
@ -1016,10 +1017,11 @@ ENTRY(\sym)
addq $EXCEPTION_STKSZ, INIT_TSS_IST(\shift_ist)
.endif
/* these procedures expect "no swapgs" flag in ebx */
.if \paranoid
jmp paranoid_exit /* %ebx: no swapgs flag */
jmp paranoid_exit
.else
jmp error_exit /* %ebx: no swapgs flag */
jmp error_exit
.endif
.if \paranoid == 1
@ -1257,8 +1259,13 @@ idtentry async_page_fault do_async_page_fault has_error_code=1
idtentry machine_check has_error_code=0 paranoid=1 do_sym=*machine_check_vector(%rip)
#endif
ENTRY(save_paranoid)
XCPT_FRAME 1 RDI+8
/*
* 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)
XCPT_FRAME 1 15*8
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
@ -1271,20 +1278,19 @@ ENTRY(save_paranoid)
xorl %ebx,%ebx
1: ret
CFI_ENDPROC
END(save_paranoid)
END(paranoid_entry)
/*
* "Paranoid" exit path from exception stack. This is invoked
* only on return from non-NMI IST interrupts that came
* from kernel space.
*
* We may be returning to very strange contexts (e.g. very early
* in syscall entry), so checking for preemption here would
* be complicated. Fortunately, we there's no good reason
* to try to handle preemption here.
*/
/* ebx: no swapgs flag */
/*
* "Paranoid" exit path from exception stack. This is invoked
* only on return from non-NMI IST interrupts that came
* from kernel space.
*
* We may be returning to very strange contexts (e.g. very early
* in syscall entry), so checking for preemption here would
* be complicated. Fortunately, we there's no good reason
* to try to handle preemption here.
*/
/* On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it) */
ENTRY(paranoid_exit)
DEFAULT_FRAME
DISABLE_INTERRUPTS(CLBR_NONE)
@ -1305,13 +1311,11 @@ paranoid_exit_restore:
END(paranoid_exit)
/*
* Exception entry point. This expects an error code/orig_rax on the stack.
* returns in "no swapgs flag" in %ebx.
* Save all registers in pt_regs, and switch gs if needed.
* Return: ebx=0: need swapgs on exit, ebx=1: otherwise
*/
ENTRY(error_entry)
XCPT_FRAME
CFI_ADJUST_CFA_OFFSET 15*8
/* oldrax contains error code */
XCPT_FRAME 1 15*8
cld
SAVE_C_REGS 8
SAVE_EXTRA_REGS 8
@ -1324,12 +1328,12 @@ error_sti:
TRACE_IRQS_OFF
ret
/*
* There are two places in the kernel that can potentially fault with
* usergs. Handle them here. B stepping K8s sometimes report a
* truncated RIP for IRET exceptions returning to compat mode. Check
* for these here too.
*/
/*
* There are two places in the kernel that can potentially fault with
* usergs. Handle them here. B stepping K8s sometimes report a
* truncated RIP for IRET exceptions returning to compat mode. Check
* for these here too.
*/
error_kernelspace:
CFI_REL_OFFSET rcx, RCX+8
incl %ebx
@ -1359,7 +1363,7 @@ error_bad_iret:
END(error_entry)
/* ebx: no swapgs flag (1: don't need swapgs, 0: need it) */
/* On entry, ebx is "no swapgs" flag (1: don't need swapgs, 0: need it) */
ENTRY(error_exit)
DEFAULT_FRAME
movl %ebx,%eax
@ -1585,13 +1589,13 @@ end_repeat_nmi:
ALLOC_PT_GPREGS_ON_STACK
/*
* Use save_paranoid to handle SWAPGS, but no need to use paranoid_exit
* Use paranoid_entry to handle SWAPGS, but no need to use paranoid_exit
* as we should not be calling schedule in NMI context.
* Even with normal interrupts enabled. An NMI should not be
* setting NEED_RESCHED or anything that normal interrupts and
* exceptions might do.
*/
call save_paranoid
call paranoid_entry
DEFAULT_FRAME 0
/*