Date: Sat, 24 Oct 2020 15:12:36 +0100 From: Salvatore Mesoraca <s.mesoraca16@...il.com> To: Topi Miettinen <toiwoton@...il.com> Cc: Kees Cook <keescook@...omium.org>, Szabolcs Nagy <szabolcs.nagy@....com>, Jeremy Linton <jeremy.linton@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, libc-alpha@...rceware.org, systemd-devel@...ts.freedesktop.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Mark Rutland <mark.rutland@....com>, Mark Brown <broonie@...nel.org>, Dave Martin <dave.martin@....com>, Catalin Marinas <Catalin.Marinas@....com>, Will Deacon <will.deacon@....com>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, linux-hardening@...r.kernel.org Subject: Re: BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures On Sat, 24 Oct 2020 at 12:34, Topi Miettinen <toiwoton@...il.com> wrote: > > On 23.10.2020 20.52, Salvatore Mesoraca wrote: > > Hi, > > > > On Thu, 22 Oct 2020 at 23:24, Topi Miettinen <toiwoton@...il.com> wrote: > >> SARA looks interesting. What is missing is a prctl() to enable all W^X > >> protections irrevocably for the current process, then systemd could > >> enable it for services with MemoryDenyWriteExecute=yes. > > > > SARA actually has a procattr interface to do just that. > > There is also a library to help using it. > > That means that /proc has to be available and writable at that point, so > setting up procattrs has to be done before mount namespaces are set up. > In general, it would be nice for sandboxing facilities in kernel if > there would be a way to start enforcing restrictions only at next > execve(), like setexeccon() for SELinux and aa_change_onexec() for > AppArmor. Otherwise the exact order of setting up various sandboxing > options can be very tricky to arrange correctly, since each option may > have a subtle effect to the sandboxing features enabled later. In case > of SARA, the operations done between shuffling the mount namespace and > before execve() shouldn't be affected so it isn't important. Even if it > did (a new sandboxing feature in the future would need trampolines or > JIT code generation), maybe the procattr file could be opened early but > it could be written closer to execve(). A new "apply on exec" procattr file seems reasonable and relatively easy to add. As Kees pointed out, the main obstacle here is the fact that SARA is not upstream :( Salvatore
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