Re: [Xen-devel] [PATCH v5 08/16] livepatch/arm/x86: Check payload for for unwelcomed symbols.

[Julien Grall <julien.grall@xxxxxxx>]

Hi Konrad,

On 21/09/16 18:32, Konrad Rzeszutek Wilk wrote:
> Certain platforms, such as ARM [32|64] add extra mapping symbols
> such as $x (for ARM64 instructions), or more interesting to
> this patch: $t (for Thumb instructions). These symbols are suppose
nit: s/are suppose to/are supposed to/

> to help the final linker to make any adjustments (such as
> add an veneer). But more importantly - we do not compile Xen
> with any Thumb instructions (which are variable length) - and
> if we find these mapping symbols we should disallow such payload.
>
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Julien Grall <julien.grall@xxxxxxx
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>
> v3: New submission.
>     Use &sym[i] instead of sym (as that will always be NULL).
> v4: Use bool instead of int for return
>     Update comment in common code about ARM odd symbols.
>     s/_check/_deny/ to make it more clear.
> v5: Also check for $t.* wildcard.
>     Use Julien's variant where we roll the [2] check in the return.
> ---
>  xen/arch/arm/livepatch.c    | 16 ++++++++++++++++
>  xen/arch/x86/livepatch.c    |  7 +++++++
>  xen/common/livepatch_elf.c  |  7 +++++++
>  xen/include/xen/livepatch.h |  2 ++
>  4 files changed, 32 insertions(+)
>
> diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c
> index 9959315..5a99ab5 100644
> --- a/xen/arch/arm/livepatch.c
> +++ b/xen/arch/arm/livepatch.c
> @@ -117,6 +117,22 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf 
> *elf,
>      return true;
>  }
>
> +bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf,
> +                                const struct livepatch_elf_sym *sym)
> +{
> +#ifdef CONFIG_ARM_32
Out of interest, is there any particular reason to use #ifdef rather 
than adding the function in {arm32/arm64}/livepatch.c?
> +    /*
> +     * Xen does not use Thumb instructions - and we should not see any of
> +     * them. If we do, abort.
> +     */
> +    if ( sym->name && sym->name[0] == '$' && sym->name[1] == 't' )
> +    {
> +        return ( !sym->name[2] || sym->name[2] == '.' );
> +    }
NIT: You could drop { } here.

> +#endif
> +    return false;
> +}
Regardless the answer to my question:

Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Regards,

--
Julien Grall

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