6.8-stable review patch. If anyone has any objections, please let me know.
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From: Josh Poimboeuf jpoimboe@kernel.org
commit 5f882f3b0a8bf0788d5a0ee44b1191de5319bb8a upstream.
While syscall hardening helps prevent some BHI attacks, there's still other low-hanging fruit remaining. Don't classify it as a mitigation and make it clear that the system may still be vulnerable if it doesn't have a HW or SW mitigation enabled.
Fixes: ec9404e40e8f ("x86/bhi: Add BHI mitigation knob") Signed-off-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Sean Christopherson seanjc@google.com Link: https://lore.kernel.org/r/b5951dae3fdee7f1520d5136a27be3bdfe95f88b.171281347... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/admin-guide/hw-vuln/spectre.rst | 11 +++++------ Documentation/admin-guide/kernel-parameters.txt | 3 +-- arch/x86/kernel/cpu/bugs.c | 6 +++--- 3 files changed, 9 insertions(+), 11 deletions(-)
--- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -441,10 +441,10 @@ The possible values in this file are: - System is protected by BHI_DIS_S * - BHI: SW loop, KVM SW loop - System is protected by software clearing sequence - * - BHI: Syscall hardening - - Syscalls are hardened against BHI - * - BHI: Syscall hardening, KVM: SW loop - - System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence + * - BHI: Vulnerable + - System is vulnerable to BHI + * - BHI: Vulnerable, KVM: SW loop + - System is vulnerable; KVM is protected by software clearing sequence
Full mitigation might require a microcode update from the CPU vendor. When the necessary microcode is not available, the kernel will @@ -661,8 +661,7 @@ kernel command line. spectre_bhi=
[X86] Control mitigation of Branch History Injection - (BHI) vulnerability. Syscalls are hardened against BHI - regardless of this setting. This setting affects the deployment + (BHI) vulnerability. This setting affects the deployment of the HW BHI control and the SW BHB clearing sequence.
on --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6033,8 +6033,7 @@ See Documentation/admin-guide/laptops/sonypi.rst
spectre_bhi= [X86] Control mitigation of Branch History Injection - (BHI) vulnerability. Syscalls are hardened against BHI - reglardless of this setting. This setting affects the + (BHI) vulnerability. This setting affects the deployment of the HW BHI control and the SW BHB clearing sequence.
--- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -2817,10 +2817,10 @@ static const char *spectre_bhi_state(voi return "; BHI: SW loop, KVM: SW loop"; else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && rrsba_disabled) return "; BHI: Retpoline"; - else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT)) - return "; BHI: Syscall hardening, KVM: SW loop"; + else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT)) + return "; BHI: Vulnerable, KVM: SW loop";
- return "; BHI: Vulnerable (Syscall hardening enabled)"; + return "; BHI: Vulnerable"; }
static ssize_t spectre_v2_show_state(char *buf)