On Wed, May 13, 2020 at 01:40:26PM +0200, Michael Kerrisk (man-pages) wrote: > Hi Dave, > > On 5/13/20 1:13 PM, Dave Martin wrote: > > On Wed, May 13, 2020 at 12:10:25PM +0200, Michael Kerrisk (man-pages) wrote: > >> Hi Dave, > >> > >> On 5/12/20 6:36 PM, Dave Martin wrote: > >>> In reality, almost every prctl interferes with assumptions that the > >>> compiler and C library / runtime rely on. prctl() can therefore > >>> make userspace explode in a variety ways that are likely to be hard > >>> to debug. > >>> > >>> This is not obvious to the uninitiated, so add a warning. > >> > >> Patch applied. But see my comments on patch 04. I may want to > >> circle back on this patch later, since the wording feels a > >> little strong to me (we simply must use prctl for some things, > >> and not all of those things break user-space/runtime as far > >> as I know). If you have some thoughts on softening the warning, > >> let me know. > > > > Certainly the "if at all" can go -- this was just a suggestion > > really. > > Yes. Gone. > > > Maybe the whole thing is superfluous. In C anything can screw up the > > runtime if you try hard enough. > > I think it's at least worth alerting the reader to this issue. > > > The background to this patch is that things like the new > > PR_PAC_RESET_KEYS and PR_SVE_SET_VL are likely to crash the program, or > > place a timebomb that will explode later when someone upgrades their > > toolchain or links with a new version of some library. Many existing > > prctls that look equally unfriendly... > > > > I didn't want to say nothing at all, but I didn't want to get into the > > gory details either. > > (Okay.) > > > Doing the digging to document the safety requirements of each prctl > > would be a lot of work, and probably an exercise in futility anyway -- > > how to use a lot of prctls safely depends on the run-time environment as > > much as it does on the kernel. > > > > > > If you want to drop this, I'm happy to add explicit notes to just the > > new arm64 prctls instead for now. > > I just softened the warning a little; see below. Explicit notes for > the new arm64 prctls would certainly be welcome. OK, that works for me. I'll try to keep it brief. Cheers ---Dave
