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| author | KP Singh <kpsingh@kernel.org> | 2023-02-27 07:05:40 +0100 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-02-27 18:57:09 +0100 |
| commit | 6921ed9049bc7457f66c1596c5b78aec0dae4a9d (patch) | |
| tree | ceb7fcf276908f10ac1b07326ebc3ab8f8f5bd8a /Documentation/admin-guide/hw-vuln/spectre.rst | |
| parent | Merge tag 'x86_cpu_for_v6.3_rc1' of git://git.kernel.org/pub/scm/linux/kernel... (diff) | |
| download | linux-6921ed9049bc7457f66c1596c5b78aec0dae4a9d.tar.xz linux-6921ed9049bc7457f66c1596c5b78aec0dae4a9d.zip | |
x86/speculation: Allow enabling STIBP with legacy IBRS
When plain IBRS is enabled (not enhanced IBRS), the logic in
spectre_v2_user_select_mitigation() determines that STIBP is not needed.
The IBRS bit implicitly protects against cross-thread branch target
injection. However, with legacy IBRS, the IBRS bit is cleared on
returning to userspace for performance reasons which leaves userspace
threads vulnerable to cross-thread branch target injection against which
STIBP protects.
Exclude IBRS from the spectre_v2_in_ibrs_mode() check to allow for
enabling STIBP (through seccomp/prctl() by default or always-on, if
selected by spectre_v2_user kernel cmdline parameter).
[ bp: Massage. ]
Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS")
Reported-by: José Oliveira <joseloliveira11@gmail.com>
Reported-by: Rodrigo Branco <rodrigo@kernelhacking.com>
Signed-off-by: KP Singh <kpsingh@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230220120127.1975241-1-kpsingh@kernel.org
Link: https://lore.kernel.org/r/20230221184908.2349578-1-kpsingh@kernel.org
Diffstat (limited to 'Documentation/admin-guide/hw-vuln/spectre.rst')
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