Commit 4d8df8cb authored Jun 07, 2020 by Anthony Steinhauser Committed by Thomas Gleixner Jun 09, 2020

x86/speculation: PR_SPEC_FORCE_DISABLE enforcement for indirect branches.



Currently, it is possible to enable indirect branch speculation even after
it was force-disabled using the PR_SPEC_FORCE_DISABLE option. Moreover, the
PR_GET_SPECULATION_CTRL command gives afterwards an incorrect result
(force-disabled when it is in fact enabled). This also is inconsistent
vs. STIBP and the documention which cleary states that
PR_SPEC_FORCE_DISABLE cannot be undone.

Fix this by actually enforcing force-disabled indirect branch
speculation. PR_SPEC_ENABLE called after PR_SPEC_FORCE_DISABLE now fails
with -EPERM as described in the documentation.

Fixes: 9137bb27 ("x86/speculation: Add prctl() control for indirect branch speculation")
Signed-off-by: Anthony Steinhauser <asteinhauser@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org

parent dbbe2ad0

arch/x86/kernel/cpu/bugs.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -1175,11 +1175,14 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
		return 0;
		/*
		* Indirect branch speculation is always disabled in strict
		* mode.
		* mode. It can neither be enabled if it was force-disabled
		* by a previous prctl call.

		*/
		if (spectre_v2_user_ibpb == SPECTRE_V2_USER_STRICT \|\|
		spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT \|\|
		spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED)
		spectre_v2_user_stibp == SPECTRE_V2_USER_STRICT_PREFERRED \|\|
		task_spec_ib_force_disable(task))
		return -EPERM;
		task_clear_spec_ib_disable(task);
		task_update_spec_tif(task);

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