linux-kernel - Re: [PATCHv3 4/7] powerpc64: Add .opd based function descriptor dereference

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Message-ID: <20171004092108.GF20084@pathway.suse.cz>
Date:   Wed, 4 Oct 2017 11:21:08 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        James Bottomley <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jessica Yu <jeyu@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 4/7] powerpc64: Add .opd based function descriptor
 dereference

On Sat 2017-09-30 11:53:16, Sergey Senozhatsky wrote:
> We are moving towards separate kernel and module function descriptor
> dereference callbacks. This patch enables it for powerpc64.
> 
> For pointers that belong to the kernel
> -  Added __start_opd and __end_opd pointers, to track the kernel
>    .opd section address range;
> 
> -  Added dereference_kernel_function_descriptor(). Now we
>    will dereference only function pointers that are within
>    [__start_opd, __end_opd];
> 
> For pointers that belong to a module
> -  Added dereference_module_function_descriptor() to handle module
>    function descriptor dereference. Now we will dereference only
>    pointers that are within [module->opd.start, module->opd.end].
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Tested-by: Helge Deller <deller@....de> # parisc64
> Tested-by: Santosh Sivaraj <santosh@...six.org> # powerpc64
> Acked-by: Michael Ellerman <mpe@...erman.id.au> # powerpc64
> Tested-by: Tony Luck <tony.luck@...el.com> # ia64
> ---
>  arch/powerpc/include/asm/module.h   |  3 +++
>  arch/powerpc/include/asm/sections.h | 11 +++++++++++
>  arch/powerpc/kernel/module_64.c     | 16 ++++++++++++++++
>  arch/powerpc/kernel/vmlinux.lds.S   |  2 ++
>  4 files changed, 32 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/module.h b/arch/powerpc/include/asm/module.h
> index 6c0132c7212f..7e28442827f1 100644
> --- a/arch/powerpc/include/asm/module.h
> +++ b/arch/powerpc/include/asm/module.h
> @@ -45,6 +45,9 @@ struct mod_arch_specific {
>  	unsigned long tramp;
>  #endif
>  
> +	/* For module function descriptor dereference */
> +	unsigned long start_opd;
> +	unsigned long end_opd;
>  #else /* powerpc64 */
>  	/* Indices of PLT sections within module. */
>  	unsigned int core_plt_section;
> diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
> index 67379b8945e8..6b4ee0d1645f 100644
> --- a/arch/powerpc/include/asm/sections.h
> +++ b/arch/powerpc/include/asm/sections.h
> @@ -75,6 +75,17 @@ static inline unsigned long dereference_function_descriptor(unsigned long ptr)
>  		ptr = (unsigned long)p;
>  	return ptr;
>  }
> +
> +#undef dereference_kernel_function_descriptor
> +static inline unsigned long
> +dereference_kernel_function_descriptor(unsigned long addr)
> +{
> +	if (addr < (unsigned long)__start_opd ||
> +			addr >= (unsigned long)__end_opd)
> +		return addr;
> +
> +	return dereference_function_descriptor(addr);
> +}
>  #endif /* PPC64_ELF_ABI_v1 */
>  
>  #endif
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 0b0f89685b67..94caec045a90 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -344,6 +344,11 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
>  		else if (strcmp(secstrings+sechdrs[i].sh_name,"__versions")==0)
>  			dedotify_versions((void *)hdr + sechdrs[i].sh_offset,
>  					  sechdrs[i].sh_size);
> +		else if (!strcmp(secstrings + sechdrs[i].sh_name, ".opd")) {
> +			me->arch.start_opd = sechdrs[i].sh_addr;
> +			me->arch.end_opd = sechdrs[i].sh_addr +
> +					   sechdrs[i].sh_size;
> +		}
>  
>  		/* We don't handle .init for the moment: rename to _init */
>  		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
> @@ -712,6 +717,17 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>  	return 0;
>  }
>  
> +#ifdef PPC64_ELF_ABI_v1
> +unsigned long dereference_module_function_descriptor(struct module *mod,
> +						     unsigned long addr)
> +{
> +	if (addr < mod->arch.start_opd || addr >= mod->arch.end_opd)
> +		return addr;
> +
> +	return dereference_function_descriptor(addr);
> +}
> +#endif /* PPC64_ELF_ABI_v1 */

I would personally move this up in the source file. It is related to
the definition of func_desc() and other functions that are
also PPC_ELF_ABI-specific.

Otherwise, it looks good to me.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr