Messages in this thread | | | From | "H.J. Lu" <> | Date | Mon, 31 Jan 2022 10:26:49 -0800 | Subject | Re: [PATCH 34/35] x86/cet/shstk: Support wrss for userspace |
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On Sun, Jan 30, 2022 at 11:57 PM Florian Weimer <fweimer@redhat.com> wrote: > > * Rick Edgecombe: > > > For the current shadow stack implementation, shadow stacks contents cannot > > be arbitrarily provisioned with data. This property helps apps protect > > themselves better, but also restricts any potential apps that may want to > > do exotic things at the expense of a little security. > > > > The x86 shadow stack feature introduces a new instruction, wrss, which > > can be enabled to write directly to shadow stack permissioned memory from > > userspace. Allow it to get enabled via the prctl interface. > > Why can't this be turned on unconditionally?
WRSS can be a security risk since it defeats the whole purpose of Shadow Stack. If an application needs to write to shadow stack, it can make a syscall to enable it. After the CET patches are checked in Linux kernel, I will make a proposal to allow applications or shared libraries to opt-in WRSS through a linker option, a compiler option or a function attribute.
-- H.J.
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