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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: 9137bb27e6 ("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
This commit is contained in:
Anthony Steinhauser 2020-06-07 05:44:19 -07:00 committed by Thomas Gleixner
parent dbbe2ad02e
commit 4d8df8cbb9
1 changed files with 5 additions and 2 deletions
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7
arch/x86/kernel/cpu/bugs.c
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@ -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);