From: Anthony Steinhauser asteinhauser@google.com
commit 4d8df8cbb9156b0a0ab3f802b80cb5db57acc0bf upstream.
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: Anthony Steinhauser asteinhauser@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/cpu/bugs.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1268,11 +1268,14 @@ static int ib_prctl_set(struct task_stru 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);