Messages in this thread | | | Date | Tue, 2 May 2023 17:53:33 -0700 | Subject | Re: [GIT PULL] x86/mm for 6.4 | From | Dave Hansen <> |
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On 5/2/23 13:14, Linus Torvalds wrote: > No, the problem is that probably *because* "access_ok()" has that > warning, not all users use "access_ok()" at all. We have places that > use "__access_ok()" instead. Like copy_from_nmi(). > > So now copy_from_nmi() doesn't do the untagging, so if you were to use > tagged pointers for the stack, you'd not get stack traces. > > End result: I think that > > (a) that WARN_ON_IN_IRQ() is actively detrimental and causes problems > > (b) the current "use untagged_addr() in access_ok()" model is also broken
Ugh, yes.
The fallout seems limited to (probably) perf and tracing poking at user stack frames. But, yes, it definitely looks broken there.
While I bet we could shoehorn the existing tlbstate checks into the __access_ok() sites, I also vastly prefer the high bit checks in access_ok() instead. The less state we have to consult, the better.
Once the WARN_ON_IN_IRQ() is gone, it seems like it's just a matter of collapsing __access_ok() into access_ok() and converting the (~3) callers.
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