Commit fe719888 authored Dec 15, 2020 by Anand K Mistry Committed by Linus Torvalds Dec 15, 2020

proc: provide details on indirect branch speculation

Similar to speculation store bypass, show information about the indirect
branch speculation mode of a task in /proc/$pid/status.

For testing/benchmarking, I needed to see whether IB (Indirect Branch)
speculation (see Spectre-v2) is enabled on a task, to see whether an
IBPB instruction should be executed on an address space switch.
Unfortunately, this information isn't available anywhere else and
currently the only way to get it is to hack the kernel to expose it
(like this change).  It also helped expose a bug with conditional IB
speculation on certain CPUs.

Another place this could be useful is to audit the system when using
sanboxing.  With this change, I can confirm that seccomp-enabled
process have IB speculation force disabled as expected when the kernel
command line parameter `spectre_v2_user=seccomp`.

Since there's already a 'Speculation_Store_Bypass' field, I used that
as precedent for adding this one.

[amistry@google.com: remove underscores from field name to workaround documentation issue]
  Link: https://lkml.kernel.org/r/20201106131015.v2.1.I7782b0cedb705384a634cfd8898eb7523562da99@changeid

Link: https://lkml.kernel.org/r/20201030172731.1.I7782b0cedb705384a634cfd8898eb7523562da99@changeid


Signed-off-by: Anand K Mistry <amistry@google.com>
Cc: Anthony Steinhauser <asteinhauser@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Anand K Mistry <amistry@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Alexey Gladkov <gladkov.alexey@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: NeilBrown <neilb@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d2928e85

Documentation/filesystems/proc.rst

+2 −0

Original line number	Diff line number	Diff line
		@@ -210,6 +210,7 @@ read the file /proc/PID/status::
		NoNewPrivs: 0
		Seccomp: 0
		Speculation_Store_Bypass: thread vulnerable
		SpeculationIndirectBranch: conditional enabled
		voluntary_ctxt_switches: 0
		nonvoluntary_ctxt_switches: 1

		@@ -292,6 +293,7 @@ It's slow but very precise.
		NoNewPrivs no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
		Seccomp seccomp mode, like prctl(PR_GET_SECCOMP, ...)
		Speculation_Store_Bypass speculative store bypass mitigation status
		SpeculationIndirectBranch indirect branch speculation mode
		Cpus_allowed mask of CPUs on which this process may run
		Cpus_allowed_list Same as previous, but in "list format"
		Mems_allowed mask of memory nodes allowed to this process

fs/proc/array.c

+28 −0

Original line number	Diff line number	Diff line
		@@ -369,6 +369,34 @@ static inline void task_seccomp(struct seq_file m, struct task_struct p)
		seq_puts(m, "vulnerable");
		break;
		}

		seq_puts(m, "\nSpeculationIndirectBranch:\t");
		switch (arch_prctl_spec_ctrl_get(p, PR_SPEC_INDIRECT_BRANCH)) {
		case -EINVAL:
		seq_puts(m, "unsupported");
		break;
		case PR_SPEC_NOT_AFFECTED:
		seq_puts(m, "not affected");
		break;
		case PR_SPEC_PRCTL \| PR_SPEC_FORCE_DISABLE:
		seq_puts(m, "conditional force disabled");
		break;
		case PR_SPEC_PRCTL \| PR_SPEC_DISABLE:
		seq_puts(m, "conditional disabled");
		break;
		case PR_SPEC_PRCTL \| PR_SPEC_ENABLE:
		seq_puts(m, "conditional enabled");
		break;
		case PR_SPEC_ENABLE:
		seq_puts(m, "always enabled");
		break;
		case PR_SPEC_DISABLE:
		seq_puts(m, "always disabled");
		break;
		default:
		seq_puts(m, "unknown");
		break;
		}
		seq_putc(m, '\n');
		}