linux-kernel - Re: [PATCH] bpf: prevent memory disambiguation attack

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Message-ID: <65f20b2e-d9d5-ca7d-6027-54a900893d6d@iogearbox.net>
Date:   Mon, 21 May 2018 23:46:31 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <ast@...nel.org>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH] bpf: prevent memory disambiguation attack

On 05/21/2018 11:17 PM, Alexei Starovoitov wrote:
> Detect code patterns where malicious 'speculative store bypass' can be used
> and sanitize such patterns.
> 
>  39: (bf) r3 = r10
>  40: (07) r3 += -216
>  41: (79) r8 = *(u64 *)(r7 +0)   // slow read
>  42: (7a) *(u64 *)(r10 -72) = 0  // verifier inserts this instruction
>  43: (7b) *(u64 *)(r8 +0) = r3   // this store becomes slow due to r8
>  44: (79) r1 = *(u64 *)(r6 +0)   // cpu speculatively executes this load
>  45: (71) r2 = *(u8 *)(r1 +0)    // speculatively arbitrary 'load byte'
>                                  // is now sanitized
> 
> Above code after x86 JIT becomes:
>  e5: mov    %rbp,%rdx
>  e8: add    $0xffffffffffffff28,%rdx
>  ef: mov    0x0(%r13),%r14
>  f3: movq   $0x0,-0x48(%rbp)
>  fb: mov    %rdx,0x0(%r14)
>  ff: mov    0x0(%rbx),%rdi
> 103: movzbq 0x0(%rdi),%rsi
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>

(No further action needed since already in Linus tree [1]. This went via the
 batch of x86 fixes on the speculative store buffer bypass from today [2].)

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=af86ca4e3088fe5eacf2f7e58c01fa68ca067672
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3b78ce4a34b761c7fe13520de822984019ff1a8f