Re: [PATCH v3 01/18] x86emul: catch exceptions occurring in stubs

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 15/02/17 11:06, Jan Beulich wrote:
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -604,14 +604,42 @@ do{ asm volatile (
>  #define __emulate_1op_8byte(_op, _dst, _eflags)
>  #endif /* __i386__ */
>  
> +#ifdef __XEN__
> +# define invoke_stub(pre, post, constraints...) do {                    \
> +    union stub_exception_token res_ = { .raw = ~0 };                    \
> +    asm volatile ( pre "\n\tcall *%[stub]\n\t" post "\n"                \
> +                   ".Lret%=:\n\t"                                       \
> +                   ".pushsection .fixup,\"ax\"\n"                       \
> +                   ".Lfix%=:\n\t"                                       \
> +                   "pop %[exn]\n\t"                                     \
> +                   "jmp .Lret%=\n\t"                                    \
> +                   ".popsection\n\t"                                    \
> +                   _ASM_EXTABLE(.Lret%=, .Lfix%=)                       \
> +                   : [exn] "+g" (res_), constraints,                    \
> +                     [stub] "rm" (stub.func) );                         \
> +    if ( unlikely(~res_.raw) )                                          \
> +    {                                                                   \
> +        gprintk(XENLOG_WARNING,                                         \
> +                "exception %u (ec=%04x) in emulation stub (line %u)\n", \
> +                res_.fields.trapnr, res_.fields.ec, __LINE__);          \

Can we also hexdump the stub here?

In the non UD case, it might also be nice to dump the GPR state, but it
is too late to be useful here, and I am not sure doing so in the
exception handler is a good idea either. 

As we manually adjust the GPR input to the stubs, the combination of the
hexdump, the exception/error code and specific stub invocation ought to
be enough information to usefully investigate with.

> +        if ( res_.fields.trapnr != EXC_UD )                             \
> +            domain_crash(current->domain);                              \

goto done?

Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

> +        else                                                            \
> +            generate_exception(EXC_UD);                                 \
> +    }                                                                   \
> +} while (0)
> +#else
> +# define invoke_stub(pre, post, constraints...)                         \
> +    asm volatile ( pre "\n\tcall *%[stub]\n\t" post                     \
> +                   : constraints, [stub] "rm" (stub.func) )
> +#endif
> +
>  #define emulate_stub(dst, src...) do {                                  \
>      unsigned long tmp;                                                  \
> -    asm volatile ( _PRE_EFLAGS("[efl]", "[msk]", "[tmp]")               \
> -                   "call *%[stub];"                                     \
> -                   _POST_EFLAGS("[efl]", "[msk]", "[tmp]")              \
> -                   : dst, [tmp] "=&r" (tmp), [efl] "+g" (_regs._eflags) \
> -                   : [stub] "r" (stub.func),                            \
> -                     [msk] "i" (EFLAGS_MASK), ## src );                 \
> +    invoke_stub(_PRE_EFLAGS("[efl]", "[msk]", "[tmp]"),                 \
> +                _POST_EFLAGS("[efl]", "[msk]", "[tmp]"),                \
> +                dst, [tmp] "=&r" (tmp), [efl] "+g" (_regs._eflags)      \
> +                : [msk] "i" (EFLAGS_MASK), ## src);                     \
>  } while (0)
>  
>  /* Fetch next part of the instruction being emulated. */


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel