On Thu 10-08-17 16:17:18, Colm MacCárthaigh wrote: > On Déar 10 Lún 2017 at 17:36 Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > On Thu 10-08-17 15:23:05, Colm MacCįrthaigh wrote: > > > On Thu, Aug 10, 2017 at 3:05 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > > >> Too late for that. VM_DONTFORK is already implemented > > > >> through MADV_DONTFORK & MADV_DOFORK, in a way that is > > > >> very similar to the MADV_WIPEONFORK from these patches. > > > > > > > > Yeah, those two seem to be breaking the "madvise as an advise" > > semantic as > > > > well but that doesn't mean we should follow that pattern any further. > > > > > > I would imagine that many of the crypto applications using > > > MADV_WIPEONFORK will also be using MADV_DONTDUMP. In cases where it's > > > for protecting secret keys, I'd like to use both in my code, for > > > example. Though that doesn't really help decide this. > > > > > > There is also at least one case for being able to turn WIPEONFORK > > > on/off with an existing page; a process that uses privilege separation > > > often goes through the following flow: > > > > > > 1. [ Access privileged keys as a power user and initialize memory ] > > > 2. [ Fork a child process that actually does the work ] > > > 3. [ Child drops privileges and uses the memory to do work ] > > > 4. [ Parent hangs around to re-spawn a child if it crashes ] > > > > > > In that mode it would be convenient to be able to mark the memory as > > > WIPEONFORK in the child, but not the parent. > > > > I am not sure I understand. The child will have an own VMA so chaging > > the attribute will not affect parent. Or did I misunderstand your > > example? > > > > Typically with privilege separation the parent has to share some minimal > state with the child. In this case that's why the page is left alone. > Though a smart parent could unset and set just immediately around the fork. > > The point then of protecting it in the child is to ensure that a grandchild > doesn't inherit the secret data. Does anybody actually do that using the minherit BSD interface? -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
