netdev - Re: [PATCH] powerpc: bpf: Fix generation of load/store DW instructions

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Date:   Sat, 16 Mar 2019 01:30:49 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Yauheni Kaliuta <yauheni.kaliuta@...hat.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH] powerpc: bpf: Fix generation of load/store DW
 instructions

On 03/15/2019 03:51 PM, Naveen N. Rao wrote:
> Yauheni Kaliuta pointed out that PTR_TO_STACK store/load verifier test
> was failing on powerpc64 BE, and rightfully indicated that the PPC_LD()
> macro is not masking away the last two bits of the offset per the ISA,
> resulting in the generation of 'lwa' instruction instead of the intended
> 'ld' instruction.
> 
> Segher also pointed out that we can't simply mask away the last two bits
> as that will result in loading/storing from/to a memory location that
> was not intended.
> 
> This patch addresses this by using ldx/stdx if the offset is not
> word-aligned. We load the offset into a temporary register (TMP_REG_2)
> and use that as the index register in a subsequent ldx/stdx. We fix
> PPC_LD() macro to mask off the last two bits, but enhance PPC_BPF_LL()
> and PPC_BPF_STL() to factor in the offset value and generate the proper
> instruction sequence. We also convert all existing users of PPC_LD() and
> PPC_STD() to use these macros. All existing uses of these macros have
> been audited to ensure that TMP_REG_2 can be clobbered.
> 
> Fixes: 156d0e290e96 ("powerpc/ebpf/jit: Implement JIT compiler for extended BPF")
> Cc: stable@...r.kernel.org # v4.9+
> 
> Reported-by: Yauheni Kaliuta <yauheni.kaliuta@...hat.com>
> Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>

Applied, thanks!