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Commit 52c419ba authored by Anthony Steinhauser's avatar Anthony Steinhauser Committed by Greg Kroah-Hartman
Browse files

x86/speculation: PR_SPEC_FORCE_DISABLE enforcement for indirect branches. 



[ Upstream commit 4d8df8cbb9156b0a0ab3f802b80cb5db57acc0bf ]

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: 9137bb27e60e ("x86/speculation: Add prctl() control for indirect branch speculation")
Signed-off-by: default avatarAnthony Steinhauser <asteinhauser@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 5d9d55cf

arch/x86/kernel/cpu/bugs.c

+5 −2
Original line number Diff line number Diff line
@@ -1249,11 +1249,14 @@ 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);