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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: ecree@solarflare.com, yhs@fb.com, daniel@iogearbox.net,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [bpf-next PATCH 05/10] bpf: verifier, return value is an int in do_refine_retval_range
Date: Wed, 25 Mar 2020 23:23:01 -0700
Message-ID: <20200326062301.fvomwkz5grg3b5qb@ast-mbp> (raw)
In-Reply-To: <158507155667.15666.4189866174878249746.stgit@john-Precision-5820-Tower>

On Tue, Mar 24, 2020 at 10:39:16AM -0700, John Fastabend wrote:
> Mark 32-bit subreg region with max value because do_refine_retval_range()
> catches functions with int return type (We will assume here that int is
> a 32-bit type). Marking 64-bit region could be dangerous if upper bits
> are not zero which could be possible.
> 
> Two reasons to pull this out of original patch. First it makes the original
> fix impossible to backport. And second I've not seen this as being problematic
> in practice unlike the other case.
> 
> Fixes: 849fa50662fbc ("bpf/verifier: refine retval R0 state for bpf_get_stack helper")
> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---
>  kernel/bpf/verifier.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 6372fa4..3731109 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4328,7 +4328,7 @@ static void do_refine_retval_range(struct bpf_reg_state *regs, int ret_type,
>  	     func_id != BPF_FUNC_probe_read_str))
>  		return;
>  
> -	ret_reg->smax_value = meta->msize_max_value;
> +	ret_reg->s32_max_value = meta->msize_max_value;

I think this is not correct.
These two special helpers are invoked via BPF_CALL_x() which has u64 return value.
So despite having 'int' return in bpf_helper_defs.h the upper 32-bit will be correct.
I think this patch should do:
ret_reg->smax_value = meta->msize_max_value;
ret_reg->s32_max_value = meta->msize_max_value;

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 17:37 [bpf-next PATCH 00/10] ALU32 bounds tracking support John Fastabend
2020-03-24 17:37 ` [bpf-next PATCH 01/10] bpf: verifier, do_refine_retval_range may clamp umin to 0 incorrectly John Fastabend
2020-03-24 17:38 ` [bpf-next PATCH 02/10] bpf: verifer, refactor adjust_scalar_min_max_vals John Fastabend
2020-03-26  6:10   ` Alexei Starovoitov
2020-03-24 17:38 ` [bpf-next PATCH 03/10] bpf: verifer, adjust_scalar_min_max_vals to always call update_reg_bounds() John Fastabend
2020-03-24 17:38 ` [bpf-next PATCH 04/10] bpf: verifier, do explicit ALU32 bounds tracking John Fastabend
2020-03-26  6:20   ` Alexei Starovoitov
2020-03-26 15:18     ` John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 05/10] bpf: verifier, return value is an int in do_refine_retval_range John Fastabend
2020-03-26  6:23   ` Alexei Starovoitov [this message]
2020-03-26 15:52     ` John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 06/10] bpf: test_progs, add test to catch retval refine error handling John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 07/10] bpf: test_verifier, bpf_get_stack return value add <0 John Fastabend
2020-03-26  6:33   ` Alexei Starovoitov
2020-03-26 15:48     ` John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 08/10] bpf: test_verifier, #70 error message updates for 32-bit right shift John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 09/10] bpf: test_verifier, #65 error message updates for trunc of boundary-cross John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 10/10] bpf: test_verifier, add alu32 bounds tracking tests John Fastabend
2020-03-26  6:34   ` Alexei Starovoitov

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