From 5ad3eb1132453b9795ce5fd4572b1c18b292cca9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 16 Feb 2022 20:57:02 +0100 Subject: Documentation/hw-vuln: Update spectre doc Update the doc with the new fun. [ bp: Massage commit message. ] Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Borislav Petkov Reviewed-by: Thomas Gleixner --- Documentation/admin-guide/hw-vuln/spectre.rst | 44 +++++++++++++++++-------- Documentation/admin-guide/kernel-parameters.txt | 8 +++-- 2 files changed, 36 insertions(+), 16 deletions(-) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst index a2b22d5640ec..79051f4dac45 100644 --- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -131,6 +131,19 @@ steer its indirect branch speculations to gadget code, and measure the speculative execution's side effects left in level 1 cache to infer the victim's data. +Yet another variant 2 attack vector is for the attacker to poison the +Branch History Buffer (BHB) to speculatively steer an indirect branch +to a specific Branch Target Buffer (BTB) entry, even if the entry isn't +associated with the source address of the indirect branch. Specifically, +the BHB might be shared across privilege levels even in the presence of +Enhanced IBRS. + +Currently the only known real-world BHB attack vector is via +unprivileged eBPF. Therefore, it's highly recommended to not enable +unprivileged eBPF, especially when eIBRS is used (without retpolines). +For a full mitigation against BHB attacks, it's recommended to use +retpolines (or eIBRS combined with retpolines). + Attack scenarios ---------------- @@ -364,13 +377,15 @@ The possible values in this file are: - Kernel status: - ==================================== ================================= - 'Not affected' The processor is not vulnerable - 'Vulnerable' Vulnerable, no mitigation - 'Mitigation: Full generic retpoline' Software-focused mitigation - 'Mitigation: Full AMD retpoline' AMD-specific software mitigation - 'Mitigation: Enhanced IBRS' Hardware-focused mitigation - ==================================== ================================= + ======================================== ================================= + 'Not affected' The processor is not vulnerable + 'Mitigation: None' Vulnerable, no mitigation + 'Mitigation: Retpolines' Use Retpoline thunks + 'Mitigation: LFENCE' Use LFENCE instructions + 'Mitigation: Enhanced IBRS' Hardware-focused mitigation + 'Mitigation: Enhanced IBRS + Retpolines' Hardware-focused + Retpolines + 'Mitigation: Enhanced IBRS + LFENCE' Hardware-focused + LFENCE + ======================================== ================================= - Firmware status: Show if Indirect Branch Restricted Speculation (IBRS) is used to protect against Spectre variant 2 attacks when calling firmware (x86 only). @@ -583,12 +598,13 @@ kernel command line. Specific mitigations can also be selected manually: - retpoline - replace indirect branches - retpoline,generic - google's original retpoline - retpoline,amd - AMD-specific minimal thunk + retpoline auto pick between generic,lfence + retpoline,generic Retpolines + retpoline,lfence LFENCE; indirect branch + retpoline,amd alias for retpoline,lfence + eibrs enhanced IBRS + eibrs,retpoline enhanced IBRS + Retpolines + eibrs,lfence enhanced IBRS + LFENCE Not specifying this option is equivalent to spectre_v2=auto. @@ -599,7 +615,7 @@ kernel command line. spectre_v2=off. Spectre variant 1 mitigations cannot be disabled. -For spectre_v2_user see :doc:`/admin-guide/kernel-parameters`. +For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt Mitigation selection guide -------------------------- diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f5a27f067db9..7123524a86b8 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -5361,8 +5361,12 @@ Specific mitigations can also be selected manually: retpoline - replace indirect branches - retpoline,generic - google's original retpoline - retpoline,amd - AMD-specific minimal thunk + retpoline,generic - Retpolines + retpoline,lfence - LFENCE; indirect branch + retpoline,amd - alias for retpoline,lfence + eibrs - enhanced IBRS + eibrs,retpoline - enhanced IBRS + Retpolines + eibrs,lfence - enhanced IBRS + LFENCE Not specifying this option is equivalent to spectre_v2=auto. -- cgit From e9b6013a7ce31535b04b02ba99babefe8a8599fa Mon Sep 17 00:00:00 2001 From: Kim Phillips Date: Mon, 28 Feb 2022 11:23:16 -0600 Subject: x86/speculation: Update link to AMD speculation whitepaper Update the link to the "Software Techniques for Managing Speculation on AMD Processors" whitepaper. Signed-off-by: Kim Phillips Signed-off-by: Borislav Petkov --- Documentation/admin-guide/hw-vuln/spectre.rst | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst index 79051f4dac45..9e9556826450 100644 --- a/Documentation/admin-guide/hw-vuln/spectre.rst +++ b/Documentation/admin-guide/hw-vuln/spectre.rst @@ -60,8 +60,8 @@ privileged data touched during the speculative execution. Spectre variant 1 attacks take advantage of speculative execution of conditional branches, while Spectre variant 2 attacks use speculative execution of indirect branches to leak privileged memory. -See :ref:`[1] ` :ref:`[5] ` :ref:`[7] ` -:ref:`[10] ` :ref:`[11] `. +See :ref:`[1] ` :ref:`[5] ` :ref:`[6] ` +:ref:`[7] ` :ref:`[10] ` :ref:`[11] `. Spectre variant 1 (Bounds Check Bypass) --------------------------------------- @@ -697,7 +697,7 @@ AMD white papers: .. _spec_ref6: -[6] `Software techniques for managing speculation on AMD processors `_. +[6] `Software techniques for managing speculation on AMD processors `_. ARM white papers: -- cgit From dd21bfa425c098b95ca86845f8e7d1ec1ddf6e4a Mon Sep 17 00:00:00 2001 From: Yun Zhou Date: Fri, 4 Mar 2022 20:29:07 -0800 Subject: proc: fix documentation and description of pagemap Since bit 57 was exported for uffd-wp write-protected (commit fb8e37f35a2f: "mm/pagemap: export uffd-wp protection information"), fixing it can reduce some unnecessary confusion. Link: https://lkml.kernel.org/r/20220301044538.3042713-1-yun.zhou@windriver.com Fixes: fb8e37f35a2fe1 ("mm/pagemap: export uffd-wp protection information") Signed-off-by: Yun Zhou Reviewed-by: Peter Xu Cc: Jonathan Corbet Cc: Tiberiu A Georgescu Cc: Florian Schmidt Cc: Ivan Teterevkov Cc: SeongJae Park Cc: Yang Shi Cc: David Hildenbrand Cc: Axel Rasmussen Cc: Miaohe Lin Cc: Andrea Arcangeli Cc: Colin Cross Cc: Alistair Popple Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/admin-guide/mm/pagemap.rst | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index bfc28704856c..6e2e416af783 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -23,7 +23,7 @@ There are four components to pagemap: * Bit 56 page exclusively mapped (since 4.2) * Bit 57 pte is uffd-wp write-protected (since 5.13) (see :ref:`Documentation/admin-guide/mm/userfaultfd.rst `) - * Bits 57-60 zero + * Bits 58-60 zero * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present -- cgit