Messages in this thread | | | Date | Tue, 7 Mar 2023 11:41:04 -0500 | Subject | Re: [PATCH net-next] net: mdio: Add netlink interface | From | Sean Anderson <> |
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On 3/7/23 08:47, Andrew Lunn wrote: > On Mon, Mar 06, 2023 at 10:48:48PM +0000, Russell King (Oracle) wrote: >> On Mon, Mar 06, 2023 at 03:45:16PM -0500, Sean Anderson wrote: >> > +static int mdio_nl_eval(struct mdio_nl_xfer *xfer) >> > +{ >> > + struct mdio_nl_insn *insn; >> > + unsigned long timeout; >> > + u16 regs[8] = { 0 }; >> > + int pc, ret = 0; >> >> So "pc" is signed. >> >> > + int phy_id, reg, prtad, devad, val; >> > + >> > + timeout = jiffies + msecs_to_jiffies(xfer->timeout_ms); >> > + >> > + mutex_lock(&xfer->mdio->mdio_lock); >> > + >> > + for (insn = xfer->prog, pc = 0; >> > + pc < xfer->prog_len; >> >> xfer->prog_len is signed, so this is a signed comparison. >> >> > + case MDIO_NL_OP_JEQ: >> > + if (__arg_ri(insn->arg0, regs) == >> > + __arg_ri(insn->arg1, regs)) >> > + pc += (s16)__arg_i(insn->arg2); >> >> This adds a signed 16-bit integer to pc, which can make pc negative. >> >> And so the question becomes... what prevents pc becoming negative >> and then trying to use a negative number as an index? > > I don't know ebpf very well, but would it of caught this? I know the > aim of this is to be simple, but due to its simplicity, we are loosing > out on all the inherent safety of eBPF. Is a eBPF interface all that > complex? I assume you just need to add some way to identify MDIO > busses and kfunc to perform a read on the bus? Regarding eBPF over netlink, the last time this was discussed, Tobias said
> - Why not use BPF? > > That could absolutely be one way forward, but the GENL approach was > easy to build out-of-tree to prove the idea. Its not obvious how it > would work though as BPF programs typically run async on some event > (probe hit, packet received etc.) whereas this is a single execution > on behalf of a user. So to what would the program be attached? The > output path is also not straight forward, but it could be done with > perf events i suppose.
I'm not familiar enough with eBPF to comment further.
--Sean
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