[seL4] Re: memory zero'ing

On Fri, Mar 10, 2023 at 3:55 PM Gerwin Klein wrote:

On 11 Mar 2023, at 09:19, Sam Leffler via Devel wrote:

I'm chasing an issue that looks like retype'd memory has nonsense data. If I read the kernel code correctly it looks like the object returned by an seL4_UntypeRetype syscall should be zero'd (looks to happen when an untyped memory object is reset here https://github.com/seL4/seL4/blob/master/src/object/untyped.c#L254). Is that correct? I don't see anything called out in the manual.

Yes, like Kent said unless it's a device untyped where the user is supposed to zero the memory, it should be 0.

One cause I could imagine would be caching (which would be a bug). E.g something like https://github.com/seL4/seL4/pull/485

Interesting. I've been validating page contents but was worried about page tables. Thanks for the pointer. -Sam