On Fri, Mar 17, 2017 at 10:19:19PM +0100, Peter Zijlstra wrote:
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -1,36 +1,70 @@
> #ifndef _ASM_X86_BUG_H
> #define _ASM_X86_BUG_H
>
> +#include <linux/stringify.h>
> +
> #define HAVE_ARCH_BUG
>
> -#ifdef CONFIG_DEBUG_BUGVERBOSE
> +/*
> + * Since some emulators terminate on UD2, we cannot use it for WARN.
> + * Since various instruction decoders disagree on the length of UD1,
> + * we cannot use it either. So use UD0 for WARN.
> + *
> + * (binutils knows about "ud1" but {en,de}codes it as 2 bytes, whereas
> + * our kernel decoder thinks it takes a ModRM byte, which seems consistent
> + * with various things like the Intel SDM instruction encoding rules)
> + */
> +
> +#define ASM_UD0 ".byte 0x0f, 0xff"
> +#define ASM_UD1 ".byte 0x0f, 0xb9" /* + ModRM */
> +#define ASM_UD2 ".byte 0x0f, 0x0b"
Thas ASM_UD1 macro isn't used anywhere.
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -169,6 +169,41 @@ void ist_end_non_atomic(void)
> preempt_disable();
> }
>
> +int is_valid_bugaddr(unsigned long addr)
> +{
> + unsigned short ud;
> +
> +#ifdef CONFIG_X86_32
> + if (addr < PAGE_OFFSET)
> + return 0;
> +#else
> + if ((long)addr > 0)
> + return 0;
> +#endif
I think comparing with TASK_SIZE would be more correct and it wouldn't
need an ifdef.
> + if (probe_kernel_address((unsigned short *)addr, ud))
> + return 0;
> +
> + return ud == 0x0b0f || ud == 0xff0f;
> +}
This code would be easier to grok if these were defines IMO.
Also, now that some of the BUG-specific functions are now also related
to WARN, they should probably be renamed to describe their new purpose,
like:
"report_bug" -> "report_bug_or_warning"
"fixup_bug" -> "fixup_bug_or_warning"
On a related note, if warn and bug are going to continue to use two
separate ud instructions for the foreseeable future, report_bug() could
be cleaned up a bit: e.g., for a ud0 instruction, it doesn't make sense
to call find_bug().
> +
> +static int fixup_bug(struct pt_regs *regs, int trapnr)
> +{
> + if (trapnr != X86_TRAP_UD)
> + return 0;
> +
> + switch (report_bug(regs->ip, regs)) {
> + case BUG_TRAP_TYPE_NONE:
> + case BUG_TRAP_TYPE_BUG:
> + break;
> +
> + case BUG_TRAP_TYPE_WARN:
> + regs->ip += 2;
> + return 1;
For self-documentation purposes, maybe use a define for the length of
the ud0 instruction?
--
Josh
