Anand K Mistry
8057e4fd7b
commit33fc379df7upstream. When spectre_v2_user={seccomp,prctl},ibpb is specified on the command line, IBPB is force-enabled and STIPB is conditionally-enabled (or not available). However, since21998a3515("x86/speculation: Avoid force-disabling IBPB based on STIBP and enhanced IBRS.") the spectre_v2_user_ibpb variable is set to SPECTRE_V2_USER_{PRCTL,SECCOMP} instead of SPECTRE_V2_USER_STRICT, which is the actual behaviour. Because the issuing of IBPB relies on the switch_mm_*_ibpb static branches, the mitigations behave as expected. Since1978b3a53a("x86/speculation: Allow IBPB to be conditionally enabled on CPUs with always-on STIBP") this discrepency caused the misreporting of IB speculation via prctl(). On CPUs with STIBP always-on and spectre_v2_user=seccomp,ibpb, prctl(PR_GET_SPECULATION_CTRL) would return PR_SPEC_PRCTL | PR_SPEC_ENABLE instead of PR_SPEC_DISABLE since both IBPB and STIPB are always on. It also allowed prctl(PR_SET_SPECULATION_CTRL) to set the IB speculation mode, even though the flag is ignored. Similarly, for CPUs without SMT, prctl(PR_GET_SPECULATION_CTRL) should also return PR_SPEC_DISABLE since IBPB is always on and STIBP is not available. [ bp: Massage commit message. ] Fixes:21998a3515("x86/speculation: Avoid force-disabling IBPB based on STIBP and enhanced IBRS.") Fixes:1978b3a53a("x86/speculation: Allow IBPB to be conditionally enabled on CPUs with always-on STIBP") Signed-off-by: Anand K Mistry <amistry@google.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: <stable@vger.kernel.org> Link: https://lkml.kernel.org/r/20201110123349.1.Id0cbf996d2151f4c143c90f9028651a5b49a5908@changeid Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.