Messages in this thread | | | Date | Sun, 10 May 2015 19:22:17 -0400 (EDT) | Subject | Re: [PATCH] ARM: net: delegate filter to kernel interpreter when imm_offset() return value can't fit into 12bits. | From | David Miller <> |
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From: Nicolas Schichan <nschichan@freebox.fr> Date: Thu, 7 May 2015 17:14:21 +0200
> 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>
Applied, thanks Nicolas.
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