lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Sun, 10 May 2020 11:48:03 +1000 From: Balbir Singh <sblbir@...zon.com> To: <tglx@...utronix.de>, <linux-kernel@...r.kernel.org> CC: <jpoimboe@...hat.com>, <tony.luck@...el.com>, <keescook@...omium.org>, <benh@...nel.crashing.org>, <x86@...nel.org>, <dave.hansen@...el.com>, <thomas.lendacky@....com>, Balbir Singh <sblbir@...zon.com> Subject: [PATCH v6 6/6] Documentation: Add L1D flushing Documentation Add documentation of l1d flushing, explain the need for the feature and how it can be used. Signed-off-by: Balbir Singh <sblbir@...zon.com> Reviewed-by: Kees Cook <keescook@...omium.org> --- Documentation/admin-guide/hw-vuln/index.rst | 1 + .../admin-guide/hw-vuln/l1d_flush.rst | 40 +++++++++++++++++++ 2 files changed, 41 insertions(+) create mode 100644 Documentation/admin-guide/hw-vuln/l1d_flush.rst diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst index 0795e3c2643f..35633b299d45 100644 --- a/Documentation/admin-guide/hw-vuln/index.rst +++ b/Documentation/admin-guide/hw-vuln/index.rst @@ -14,3 +14,4 @@ are configurable at compile, boot or run time. mds tsx_async_abort multihit.rst + l1d_flush diff --git a/Documentation/admin-guide/hw-vuln/l1d_flush.rst b/Documentation/admin-guide/hw-vuln/l1d_flush.rst new file mode 100644 index 000000000000..7d515b8c29f1 --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/l1d_flush.rst @@ -0,0 +1,40 @@ +L1D Flushing for the paranoid +============================= + +With an increasing number of vulnerabilities being reported around data +leaks from L1D, a new user space mechanism to flush the L1D cache on +context switch is added to the kernel. This should help address +CVE-2020-0550 and for paranoid applications, keep them safe from any +yet to be discovered vulnerabilities, related to leaks from the L1D +cache. + +Tasks can opt in to this mechanism by using a prctl (implemented only +for x86 at the moment). + +Related CVES +------------ +At the present moment, the following CVEs can be addressed by this +mechanism + + ============= ======================== ================== + CVE-2020-0550 Improper Data Forwarding OS related aspects + ============= ======================== ================== + +Usage Guidelines +---------------- +Applications can call ``prctl(2)`` with one of these two arguments + +1. PR_SET_L1D_FLUSH - flush the L1D cache on context switch (out) +2. PR_GET_L1D_FLUSH - get the current state of the L1D cache flush, returns 1 + if set and 0 if not set. + +**NOTE**: The feature is disabled by default, applications to need to specifically +opt into the feature to enable it. + +Mitigation +---------- +When PR_SET_L1D_FLUSH is enabled for a task, on switching tasks (when +the address space changes), a flush of the L1D cache is performed for +the task when it leaves the CPU. If the underlying CPU supports L1D +flushing in hardware, the hardware mechanism is used, otherwise a software +fallback, similar to the mechanism used by L1TF is used. -- 2.17.1
Powered by blists - more mailing lists