diff options
| author | Kim Phillips <kim.phillips@amd.com> | 2023-07-20 14:47:27 -0500 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-07-22 18:04:22 +0200 |
| commit | fd470a8beed88440b160d690344fbae05a0b9b1b (patch) | |
| tree | 2355c8b0ee8742bf5c8c5f121450734bb3bf97e0 /Documentation/admin-guide/hw-vuln | |
| parent | 3ba2e83334bed2b1980b59734e6e84dfaf96026c (diff) | |
x86/cpu: Enable STIBP on AMD if Automatic IBRS is enabled
Unlike Intel's Enhanced IBRS feature, AMD's Automatic IBRS does not
provide protection to processes running at CPL3/user mode, see section
"Extended Feature Enable Register (EFER)" in the APM v2 at
https://bugzilla.kernel.org/attachment.cgi?id=304652
Explicitly enable STIBP to protect against cross-thread CPL3
branch target injections on systems with Automatic IBRS enabled.
Also update the relevant documentation.
Fixes: e7862eda309e ("x86/cpu: Support AMD Automatic IBRS")
Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230720194727.67022-1-kim.phillips@amd.com
Diffstat (limited to 'Documentation/admin-guide/hw-vuln')
| -rw-r--r-- | Documentation/admin-guide/hw-vuln/spectre.rst | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst index 4d186f599d90..32a8893e5617 100644 --- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -484,11 +484,14 @@ Spectre variant 2 Systems which support enhanced IBRS (eIBRS) enable IBRS protection once at boot, by setting the IBRS bit, and they're automatically protected against - Spectre v2 variant attacks, including cross-thread branch target injections - on SMT systems (STIBP). In other words, eIBRS enables STIBP too. + Spectre v2 variant attacks. - Legacy IBRS systems clear the IBRS bit on exit to userspace and - therefore explicitly enable STIBP for that + On Intel's enhanced IBRS systems, this includes cross-thread branch target + injections on SMT systems (STIBP). In other words, Intel eIBRS enables + STIBP, too. + + AMD Automatic IBRS does not protect userspace, and Legacy IBRS systems clear + the IBRS bit on exit to userspace, therefore both explicitly enable STIBP. The retpoline mitigation is turned on by default on vulnerable CPUs. It can be forced on or off by the administrator |