path: root/arch/arm64
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authorDaniel Borkmann <daniel@iogearbox.net>2015-12-17 23:51:54 +0100
committerDavid S. Miller <davem@davemloft.net>2015-12-18 16:04:51 -0500
commit8b614aebecdf2b1f72d51b1527f5a75d218b78e2 (patch)
tree4ac23e78eaa9111f694ac114b0ec04c071ab0a9e /arch/arm64
parentbpf: add bpf_skb_load_bytes helper (diff)
bpf: move clearing of A/X into classic to eBPF migration prologue
Back in the days where eBPF (or back then "internal BPF" ;->) was not exposed to user space, and only the classic BPF programs internally translated into eBPF programs, we missed the fact that for classic BPF A and X needed to be cleared. It was fixed back then via 83d5b7ef99c9 ("net: filter: initialize A and X registers"), and thus classic BPF specifics were added to the eBPF interpreter core to work around it. This added some confusion for JIT developers later on that take the eBPF interpreter code as an example for deriving their JIT. F.e. in f75298f5c3fe ("s390/bpf: clear correct BPF accumulator register"), at least X could leak stack memory. Furthermore, since this is only needed for classic BPF translations and not for eBPF (verifier takes care that read access to regs cannot be done uninitialized), more complexity is added to JITs as they need to determine whether they deal with migrations or native eBPF where they can just omit clearing A/X in their prologue and thus reduce image size a bit, see f.e. cde66c2d88da ("s390/bpf: Only clear A and X for converted BPF programs"). In other cases (x86, arm64), A and X is being cleared in the prologue also for eBPF case, which is unnecessary. Lets move this into the BPF migration in bpf_convert_filter() where it actually belongs as long as the number of eBPF JITs are still few. It can thus be done generically; allowing us to remove the quirk from __bpf_prog_run() and to slightly reduce JIT image size in case of eBPF, while reducing code duplication on this matter in current(/future) eBPF JITs. Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Alexei Starovoitov <ast@kernel.org> Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com> Tested-by: Michael Holzheu <holzheu@linux.vnet.ibm.com> Cc: Zi Shen Lim <zlim.lnx@gmail.com> Cc: Yang Shi <yang.shi@linaro.org> Acked-by: Yang Shi <yang.shi@linaro.org> Acked-by: Zi Shen Lim <zlim.lnx@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch/arm64')
1 files changed, 0 insertions, 6 deletions
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index b162ad70effc..7658612d915c 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -152,8 +152,6 @@ static void build_prologue(struct jit_ctx *ctx)
const u8 r8 = bpf2a64[BPF_REG_8];
const u8 r9 = bpf2a64[BPF_REG_9];
const u8 fp = bpf2a64[BPF_REG_FP];
- const u8 ra = bpf2a64[BPF_REG_A];
- const u8 rx = bpf2a64[BPF_REG_X];
const u8 tmp1 = bpf2a64[TMP_REG_1];
const u8 tmp2 = bpf2a64[TMP_REG_2];
@@ -200,10 +198,6 @@ static void build_prologue(struct jit_ctx *ctx)
/* Set up function call stack */
emit(A64_SUB_I(1, A64_SP, A64_SP, STACK_SIZE), ctx);
- /* Clear registers A and X */
- emit_a64_mov_i64(ra, 0, ctx);
- emit_a64_mov_i64(rx, 0, ctx);
static void build_epilogue(struct jit_ctx *ctx)