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Mandatory enforcement of indirect branch targets

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Re: Mandatory enforcement of indirect branch targets

#11

Post by redundantly »

SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

I wouldn't have it any other way. I love the OpenBSD mailing lists. Always an entertaining read when Theo gets involved.

Re: Mandatory enforcement of indirect branch targets

#12

Post by teknopurge »

redundantly wrote: post #11
SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

I wouldn't have it any other way. I love the OpenBSD mailing lists. Always an entertaining read when Theo gets involved.

upvoted and +1. Theo has been an important leader in OSS for decades: his brevity and impatience is a net positive. also he is usually correct.

Re: Mandatory enforcement of indirect branch targets

#13

Post by Joker_vD »

SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

That's the problem with many brilliant people: what they perceive as their interlocutors being deliberately obtuse on some completely obvious point is actually their interlocutors being just as smart as they always are on some point that is not obvious at all to them.

Re: Mandatory enforcement of indirect branch targets

#15

Post by codedokode »

messe wrote: post #2

For anybody unfamiliar with this, as I was, this appears to refer to Intel's Indirect Branch Tracking feature[1] (and the equivalent on ARM, BTI). The idea is that an indirect branch can only pass control to a location that starts with an "end branch" instruction. An indirect branch is one that jumps to a location whose value is loaded or computed from either a register or memory address: think calling a function poi…

Why should every function start with endbr64 command? Aren't functions usually called directly?

Also, is it required to insert endbr64 command after function calls (for return address)?

Re: Mandatory enforcement of indirect branch targets

#16

Post by Ericson2314 »

SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

Are Theo and Linux more alike than OpenBSD and Linux?

Re: Mandatory enforcement of indirect branch targets

#17

Post by rkangel »

Joker_vD wrote: post #13
SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

That's the problem with many brilliant people: what they perceive as their interlocutors being deliberately obtuse on some completely obvious point is actually their interlocutors being just as smart as they always are on some point that is not obvious at all to them.

Perception of relative intelligence or sensible decision making is irrelevant. Just because you think you're doing a better job doesn't mean you need to shit on the other person.

You could not mention Linux at all, or you could even say "we think this is better than Linux's approach because of X" and it would be a great improvement.

I have always found it interesting that Rust purposefully avoided doing language comparisons - "we're better than Python like this and better than C like that". Their message purposefully avoided any positioning of it as a competition, instead focusing just on articulating Rust's value. It was an eye opening approach given our instinct is normally to pit things against each other.

Re: Mandatory enforcement of indirect branch targets

#18

Post by messe »

codedokode wrote: post #15
messe wrote: post #2

For anybody unfamiliar with this, as I was, this appears to refer to Intel's Indirect Branch Tracking feature[1] (and the equivalent on ARM, BTI). The idea is that an indirect branch can only pass control to a location that starts with an "end branch" instruction. An indirect branch is one that jumps to a location whose value is loaded or computed from either a register or memory address: think calling a function poi…

Why should every function start with endbr64 command? Aren't functions usually called directly? Also, is it required to insert endbr64 command after function calls (for return address)?

C allows for any function to be called via a function pointer, and functions can be in different translation units, so the compiler can't simply assume that a function will never be called indirectly and has to pessimistically insert endbr64 in order to maintain a reasonable ABI.

And no, as I understand it, this is only for branch/calls not returns.

Re: Mandatory enforcement of indirect branch targets

#19

Post by gcoakes »

messe wrote: post #9
rollcat wrote: post #8

Earlier quoted context omitted.

Various architectures do other interesting things with NOPs, IIRC one convention on PowerPC had something vaguely related to debugging or tracing (I can't remember the details or find any references right now).

Not just architectures, but different OSes and ABIs have found ways to repurpose no-ops. One example[1] is Windows using the 2-byte "MOV EDI, EDI" as a hot-patch point: it gets replaced by a "JMP $-5" instruction which jumps 5 bytes before the start of a function into a spot reserved for patching. That 5 bytes is enough to contain a full jump instruction that can then jump wherever you need it to. ## Why do Windows f…

Good read. Thank you.

This just worsens my fear of changing "unnecessary" code when I don't know the original motivation for it.

Re: Mandatory enforcement of indirect branch targets

#20

Post by PrimeMcFly »

Ericson2314 wrote: post #16
SoftTalker wrote: post #10

Theo had to get his digs in against Linux in that announcement. Why not just focus on what OpenBSD is doing, and maybe contrast it to what Linux does without the speculation that they will still be doing the same thing in 20 years. He's unquestionably brilliant, but I've had a few encounters with him on the mailing lists and he is so quick to take offense where none was meant and drop into name-calling and insults. I…

Are Theo and Linux more alike than OpenBSD and Linux?

Now, yes. Linus wasn't always so abrasive though. At some point he caught up to Theo.
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