netdev - Re: [PATCH bpf 1/3] bpf: restrict bpf_probe_read{,str}() only to archs where they work

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Date:   Fri, 15 May 2020 09:06:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     ast@...nel.org, bpf@...r.kernel.org, netdev@...r.kernel.org,
        torvalds@...ux-foundation.org, mhiramat@...nel.org,
        brendan.d.gregg@...il.com, hch@....de, john.fastabend@...il.com,
        yhs@...com
Subject: Re: [PATCH bpf 1/3] bpf: restrict bpf_probe_read{,str}() only to
 archs where they work

On Thu, 14 May 2020 18:16:05 +0200
Daniel Borkmann <daniel@...earbox.net> wrote:

> Given the legacy bpf_probe_read{,str}() BPF helpers are broken on archs
> with overlapping address ranges, we should really take the next step to
> disable them from BPF use there.
> 
> To generally fix the situation, we've recently added new helper variants
> bpf_probe_read_{user,kernel}() and bpf_probe_read_{user,kernel}_str().
> For details on them, see 6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel}
> and probe_read_{user,kernel}_str helpers").
> 
> Given bpf_probe_read{,str}() have been around for ~5 years by now, there
> are plenty of users at least on x86 still relying on them today, so we
> cannot remove them entirely w/o breaking the BPF tracing ecosystem.
> 
> However, their use should be restricted to archs with non-overlapping
> address ranges where they are working in their current form. Therefore,
> move this behind a CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE and
> have x86, arm64, arm select it (other archs supporting it can follow-up
> on it as well).
> 
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Brendan Gregg <brendan.d.gregg@...il.com>
> Cc: Christoph Hellwig <hch@....de>

Thanks for the config! Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>


> ---
>  arch/arm/Kconfig         | 1 +
>  arch/arm64/Kconfig       | 1 +
>  arch/x86/Kconfig         | 1 +
>  init/Kconfig             | 3 +++
>  kernel/trace/bpf_trace.c | 6 ++++--
>  5 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 66a04f6f4775..c77c93c485a0 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -12,6 +12,7 @@ config ARM
>  	select ARCH_HAS_KEEPINITRD
>  	select ARCH_HAS_KCOV
>  	select ARCH_HAS_MEMBARRIER_SYNC_CORE
> +	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>  	select ARCH_HAS_PTE_SPECIAL if ARM_LPAE
>  	select ARCH_HAS_PHYS_TO_DMA
>  	select ARCH_HAS_SETUP_DMA_OPS
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 40fb05d96c60..5d513f461957 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -20,6 +20,7 @@ config ARM64
>  	select ARCH_HAS_KCOV
>  	select ARCH_HAS_KEEPINITRD
>  	select ARCH_HAS_MEMBARRIER_SYNC_CORE
> +	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>  	select ARCH_HAS_PTE_DEVMAP
>  	select ARCH_HAS_PTE_SPECIAL
>  	select ARCH_HAS_SETUP_DMA_OPS
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 1197b5596d5a..2d3f963fd6f1 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -68,6 +68,7 @@ config X86
>  	select ARCH_HAS_KCOV			if X86_64
>  	select ARCH_HAS_MEM_ENCRYPT
>  	select ARCH_HAS_MEMBARRIER_SYNC_CORE
> +	select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
>  	select ARCH_HAS_PMEM_API		if X86_64
>  	select ARCH_HAS_PTE_DEVMAP		if X86_64
>  	select ARCH_HAS_PTE_SPECIAL
> diff --git a/init/Kconfig b/init/Kconfig
> index 9e22ee8fbd75..6fd13a051342 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -2279,6 +2279,9 @@ config ASN1
>  
>  source "kernel/Kconfig.locks"
>  
> +config ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> +	bool
> +
>  config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
>  	bool
>  
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index ca1796747a77..b83bdaa31c7b 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -825,14 +825,16 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>  		return &bpf_probe_read_user_proto;
>  	case BPF_FUNC_probe_read_kernel:
>  		return &bpf_probe_read_kernel_proto;
> -	case BPF_FUNC_probe_read:
> -		return &bpf_probe_read_compat_proto;
>  	case BPF_FUNC_probe_read_user_str:
>  		return &bpf_probe_read_user_str_proto;
>  	case BPF_FUNC_probe_read_kernel_str:
>  		return &bpf_probe_read_kernel_str_proto;
> +#ifdef CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> +	case BPF_FUNC_probe_read:
> +		return &bpf_probe_read_compat_proto;
>  	case BPF_FUNC_probe_read_str:
>  		return &bpf_probe_read_compat_str_proto;
> +#endif
>  #ifdef CONFIG_CGROUPS
>  	case BPF_FUNC_get_current_cgroup_id:
>  		return &bpf_get_current_cgroup_id_proto;
> -- 
> 2.21.0
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>