** Changed in: linux (Ubuntu Noble)
Status: New => Fix Committed
** Description changed:
[Impact]
Branch History Injection (BHI) attacks may allow a malicious application
to influence indirect branch prediction in kernel by poisoning the
branch history. eIBRS isolates indirect branch targets in ring0.
The BHB can still influence the choice of indirect branch predictor
entry, and although branch predictor entries are isolated between modes
when eIBRS is enabled, the BHB itself is not isolated between modes.
Previously the only known real-world BHB attack vector was via
unprivileged eBPF. Further research has found attacks that don't require
unprivileged eBPF.
+ See also:
+ https://www.phoronix.com/news/Linux-BHI-Branch-History-Inject
+
[Test case]
https://www.vusec.net/projects/native-bhi/
[Fix]
Backport from upstream the merge that introduces spectre_bhi= boot
option to control BHI mitigation:
- 2bb69f5fc721 ("Merge tag 'nativebhi' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
- ed2e8d49b54d ("KVM: x86: Add BHI_NO")
- 95a6ccbdc719 ("x86/bhi: Mitigate KVM by default")
- ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
- be482ff95009 ("x86/bhi: Enumerate Branch History Injection (BHI) bug")
- 0f4a837615ff ("x86/bhi: Define SPEC_CTRL_BHI_DIS_S")
- 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall
entry")
- 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system
calls")
- 0cd01ac5dcb1 ("x86/bugs: Change commas to semicolons in 'spectre_v2' sysfs
file")
+ 2bb69f5fc721 ("Merge tag 'nativebhi' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
+ ed2e8d49b54d ("KVM: x86: Add BHI_NO")
+ 95a6ccbdc719 ("x86/bhi: Mitigate KVM by default")
+ ec9404e40e8f ("x86/bhi: Add BHI mitigation knob")
+ be482ff95009 ("x86/bhi: Enumerate Branch History Injection (BHI) bug")
+ 0f4a837615ff ("x86/bhi: Define SPEC_CTRL_BHI_DIS_S")
+ 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall
entry")
+ 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system
calls")
+ 0cd01ac5dcb1 ("x86/bugs: Change commas to semicolons in 'spectre_v2' sysfs
file")
Also set spectre_bhi=auto by default, that will rely on the BHI_DIS_S
hardware control if it's available on the system CPUs, otherwise a
proper software sequence will be deployed at VMexit.
[Regression potential]
We may experience performance regressions with this new mitigation
enabled, especially in VMs and CPUs that don't have the BHI hardware
support capability (due to the extra software sequence executed at
VMexit).
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https://bugs.launchpad.net/bugs/2060909
Title:
Backport mitigations for the native BHI hardware vulnerabilty
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