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From: Eric Biggers <ebiggers@kernel.org>
To: Edward Cree <ecree.xilinx@gmail.com>
Cc: Kurt Manucredo <fuzzybritches0@gmail.com>,
	syzbot+bed360704c521841c85d@syzkaller.appspotmail.com,
	keescook@chromium.org, yhs@fb.com, dvyukov@google.com,
	andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org,
	daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org,
	john.fastabend@gmail.com, kafai@fb.com, kpsingh@kernel.org,
	kuba@kernel.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, songliubraving@fb.com,
	syzkaller-bugs@googlegroups.com, nathan@kernel.org,
	ndesaulniers@google.com, clang-built-linux@googlegroups.com,
	kernel-hardening@lists.openwall.com, kasan-dev@googlegroups.com
Subject: Re: [PATCH v5] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run
Date: Tue, 15 Jun 2021 12:33:00 -0700	[thread overview]
Message-ID: <YMkAbNQiIBbhD7+P@gmail.com> (raw)
In-Reply-To: <bac16d8d-c174-bdc4-91bd-bfa62b410190@gmail.com>

On Tue, Jun 15, 2021 at 07:51:07PM +0100, Edward Cree wrote:
> 
> As I understand it, the UBSAN report is coming from the eBPF interpreter,
>  which is the *slow path* and indeed on many production systems is
>  compiled out for hardening reasons (CONFIG_BPF_JIT_ALWAYS_ON).
> Perhaps a better approach to the fix would be to change the interpreter
>  to compute "DST = DST << (SRC & 63);" (and similar for other shifts and
>  bitnesses), thus matching the behaviour of most chips' shift opcodes.
> This would shut up UBSAN, without affecting JIT code generation.
> 

Yes, I suggested that last week
(https://lkml.kernel.org/netdev/YMJvbGEz0xu9JU9D@gmail.com).  The AND will even
get optimized out when compiling for most CPUs.

- Eric

  reply	other threads:[~2021-06-15 19:33 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <000000000000c2987605be907e41@google.com>
     [not found] ` <20210602212726.7-1-fuzzybritches0@gmail.com>
     [not found]   ` <YLhd8BL3HGItbXmx@kroah.com>
     [not found]     ` <87609-531187-curtm@phaethon>
     [not found]       ` <6a392b66-6f26-4532-d25f-6b09770ce366@fb.com>
     [not found]         ` <CAADnVQKexxZQw0yK_7rmFOdaYabaFpi2EmF6RGs5bXvFHtUQaA@mail.gmail.com>
2021-06-07  7:38           ` [PATCH v4] bpf: core: fix shift-out-of-bounds in ___bpf_prog_run Dmitry Vyukov
2021-06-09 18:20             ` Kees Cook
2021-06-09 23:40               ` Yonghong Song
2021-06-10  5:32                 ` Dmitry Vyukov
2021-06-10  6:06                   ` Yonghong Song
2021-06-10 17:06                     ` Kees Cook
2021-06-10 17:52                       ` Alexei Starovoitov
2021-06-10 20:00                         ` Eric Biggers
2021-06-15 16:42                           ` [PATCH v5] " Kurt Manucredo
2021-06-15 18:51                             ` Edward Cree
2021-06-15 19:33                               ` Eric Biggers [this message]
2021-06-15 21:08                                 ` Daniel Borkmann
2021-06-15 21:32                                   ` Eric Biggers
2021-06-15 21:38                                     ` Eric Biggers
2021-06-15 21:54                                       ` Daniel Borkmann
2021-06-15 22:07                                         ` Eric Biggers
2021-06-15 22:31                                           ` Kurt Manucredo
2021-06-17 10:09                                           ` Daniel Borkmann

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