Messages in this thread | | | Date | Thu, 07 May 2015 18:18:08 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH] ARM: net: delegate filter to kernel interpreter when imm_offset() return value can't fit into 12bits. |
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On 05/07/2015 05:14 PM, Nicolas Schichan wrote: > The ARM JIT code emits "ldr rX, [pc, #offset]" to access the literal > pool. #offset maximum value is 4095 and if the generated code is too > large, the #offset value can overflow and not point to the expected > slot in the literal pool. Additionally, when overflow occurs, bits of > the overflow can end up changing the destination register of the ldr > instruction. > > Fix that by detecting the overflow in imm_offset() and setting a flag > that is checked for each BPF instructions converted in > build_body(). As of now it can only be detected in the second pass. As > a result the second build_body() call can now fail, so add the > corresponding cleanup code in that case. > > Using multiple literal pools in the JITed code is going to require > lots of intrusive changes to the JIT code (which would better be done > as a feature instead of fix), just delegating to the kernel BPF > interpreter in that case is a more straight forward, minimal fix and > easy to backport. > > Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
Fix looks good to me.
Fixes: ddecdfcea0ae ("ARM: 7259/3: net: JIT compiler for packet filters") Acked-by: Daniel Borkmann <daniel@iogearbox.net>
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