netdev - Re: [PATCH bpf-next 1/2] bpf: extend stackmap to save binary_build

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180305162622.GC25181@hirez.programming.kicks-ass.net>
Date:   Mon, 5 Mar 2018 17:26:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        kernel-team@...com, hannes@...xchg.org, riel@...riel.com
Subject: Re: [PATCH bpf-next 1/2] bpf: extend stackmap to save
 binary_build_id+offset instead of address

On Mon, Feb 26, 2018 at 09:49:22AM -0800, Song Liu wrote:

> +/* Parse build ID of ELF file mapped to vma */
> +static int stack_map_get_build_id(struct vm_area_struct *vma,
> +				  unsigned char *build_id)
> +{
> +	Elf32_Ehdr *ehdr = (Elf32_Ehdr *)vma->vm_start;

How does this work? Isn't vma->vm_start a _user_ address?

> +
> +	/* we need at least 1 file header and 1 program header */
> +	if (vma->vm_end - vma->vm_start <
> +	    sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr))
> +		return -EINVAL;
> +
> +	/* compare magic x7f "ELF" */
> +	if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
> +		return -EINVAL;

So how come you can just dereference it here, without
get_user()/copy_from_user() etc.. ?

> +
> +	/* only support executable file and shared object file */
> +	if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
> +		return -EINVAL;
> +
> +	if (ehdr->e_ident[EI_CLASS] == 1)
> +		return stack_map_get_build_id_32(vma, build_id);
> +	else if (ehdr->e_ident[EI_CLASS] == 2)
> +		return stack_map_get_build_id_64(vma, build_id);
> +	return -EINVAL;
> +}