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Date: Wed, 8 Feb 2017 10:43:13 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Kees Cook <keescook@...omium.org>,
	"Reshetova, Elena" <elena.reshetova@...el.com>,
	Greg KH <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <h.peter.anvin@...el.com>,
	Will Deacon <will.deacon@....com>,
	David Windsor <dwindsor@...il.com>,
	Hans Liljestrand <ishkamiel@...il.com>,
	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: Re: [PATCH 4/4] refcount: Report failures
 through CHECK_DATA_CORRUPTION

On Wed, Feb 08, 2017 at 10:12:50AM +0100, Peter Zijlstra wrote:
> Something like:
> 
> #define EX_REG_HANDLER(_reg)					\
> bool ex_handler_value_##_reg(const struct exception_table_entry *fixup, \
> 			    struct pt_regs *regs, int trapnr)	\
> {								\
> 	void (*handler)(unsigned long) =			\
> 		(void *)((unsigned long)&fixup->to + fixup->to); \
> 								\
> 	if (trapnr != X86_TRAP_UD)				\
> 		return false;					\
> 								\
> 	regs->ip += 2; /* size of UD2 instruction */		\
> 	handler(regs->_reg);					\
> 	return true;						\
> }
> 
> EX_REG_HANDLER(bx);
> EX_REG_HANDLER(cx);
> ...
> EX_REG_HANDLER(ss);
> 
> 
> asm (
> " .macro reg_to_handler	r\n"
> " .irp rs,bx,cx,...,ss\n"
> " .ifc \\r, %\\rs\n"
> " ex_handler_value_\\rs\n"
> " .endif\n"
  " .ifc \\r, %e\\rs\n"
  " ex_handler_value_\\rs\n"
  " .endif\n"
  " .ifc \\r, %r\\rs\n"
  " ex_handler_value_\\rs\n"
  " .endif\n"
> " .endr\n"
> " .endm\n"
> );

to match the 16, 32 and 64 bit names of the same registers. The byte
registers will need additional magic :/


> #define EXCEPTION_VALUE(val, handler)			\
> 	asm volatile ("1: ud2"				\
> 		      _ASM_EXTABLE_HANDLE(1b, handler,	\
> 				     reg_to_handler %0) \
> 		      : : "r" (val))
> 
> 
> Where the generic version can simply be:
> 
> #define EXCEPTION_VALUE(val, handler)	handler((unsigned long)val)
> 
> 
> Makes sense?

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