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-rw-r--r--Documentation/ABI/testing/sysfs-devices-system-cpu16
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt58
-rw-r--r--Documentation/filesystems/nilfs2.txt4
-rw-r--r--Documentation/kbuild/kconfig-language.txt23
-rw-r--r--Documentation/usb/gadget-testing.txt2
-rw-r--r--Documentation/x86/pti.txt186
6 files changed, 268 insertions, 21 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index d6d862db3b5d..bfd29bc8d37a 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -375,3 +375,19 @@ Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: information about CPUs heterogeneity.
cpu_capacity: capacity of cpu#.
+
+What: /sys/devices/system/cpu/vulnerabilities
+ /sys/devices/system/cpu/vulnerabilities/meltdown
+ /sys/devices/system/cpu/vulnerabilities/spectre_v1
+ /sys/devices/system/cpu/vulnerabilities/spectre_v2
+Date: January 2018
+Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
+Description: Information about CPU vulnerabilities
+
+ The files are named after the code names of CPU
+ vulnerabilities. The output of those files reflects the
+ state of the CPUs in the system. Possible output values:
+
+ "Not affected" CPU is not affected by the vulnerability
+ "Vulnerable" CPU is affected and no mitigation in effect
+ "Mitigation: $M" CPU is affected and mitigation $M is in effect
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index af7104aaffd9..46b26bfee27b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -713,9 +713,6 @@
It will be ignored when crashkernel=X,high is not used
or memory reserved is below 4G.
- crossrelease_fullstack
- [KNL] Allow to record full stack trace in cross-release
-
cryptomgr.notests
[KNL] Disable crypto self-tests
@@ -2626,6 +2623,11 @@
nosmt [KNL,S390] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
+ nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
+ (indirect branch prediction) vulnerability. System may
+ allow data leaks with this option, which is equivalent
+ to spectre_v2=off.
+
noxsave [BUGS=X86] Disables x86 extended register state save
and restore using xsave. The kernel will fallback to
enabling legacy floating-point and sse state.
@@ -2712,8 +2714,6 @@
steal time is computed, but won't influence scheduler
behaviour
- nopti [X86-64] Disable kernel page table isolation
-
nolapic [X86-32,APIC] Do not enable or use the local APIC.
nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
@@ -3100,6 +3100,12 @@
pcie_scan_all Scan all possible PCIe devices. Otherwise we
only look for one device below a PCIe downstream
port.
+ big_root_window Try to add a big 64bit memory window to the PCIe
+ root complex on AMD CPUs. Some GFX hardware
+ can resize a BAR to allow access to all VRAM.
+ Adding the window is slightly risky (it may
+ conflict with unreported devices), so this
+ taints the kernel.
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
Management.
@@ -3288,11 +3294,20 @@
pt. [PARIDE]
See Documentation/blockdev/paride.txt.
- pti= [X86_64]
- Control user/kernel address space isolation:
- on - enable
- off - disable
- auto - default setting
+ pti= [X86_64] Control Page Table Isolation of user and
+ kernel address spaces. Disabling this feature
+ removes hardening, but improves performance of
+ system calls and interrupts.
+
+ on - unconditionally enable
+ off - unconditionally disable
+ auto - kernel detects whether your CPU model is
+ vulnerable to issues that PTI mitigates
+
+ Not specifying this option is equivalent to pti=auto.
+
+ nopti [X86_64]
+ Equivalent to pti=off
pty.legacy_count=
[KNL] Number of legacy pty's. Overwrites compiled-in
@@ -3943,6 +3958,29 @@
sonypi.*= [HW] Sony Programmable I/O Control Device driver
See Documentation/laptops/sonypi.txt
+ spectre_v2= [X86] Control mitigation of Spectre variant 2
+ (indirect branch speculation) vulnerability.
+
+ on - unconditionally enable
+ off - unconditionally disable
+ auto - kernel detects whether your CPU model is
+ vulnerable
+
+ Selecting 'on' will, and 'auto' may, choose a
+ mitigation method at run time according to the
+ CPU, the available microcode, the setting of the
+ CONFIG_RETPOLINE configuration option, and the
+ compiler with which the kernel was built.
+
+ Specific mitigations can also be selected manually:
+
+ retpoline - replace indirect branches
+ retpoline,generic - google's original retpoline
+ retpoline,amd - AMD-specific minimal thunk
+
+ Not specifying this option is equivalent to
+ spectre_v2=auto.
+
spia_io_base= [HW,MTD]
spia_fio_base=
spia_pedr=
diff --git a/Documentation/filesystems/nilfs2.txt b/Documentation/filesystems/nilfs2.txt
index c0727dc36271..f2f3f8592a6f 100644
--- a/Documentation/filesystems/nilfs2.txt
+++ b/Documentation/filesystems/nilfs2.txt
@@ -25,8 +25,8 @@ available from the following download page. At least "mkfs.nilfs2",
cleaner or garbage collector) are required. Details on the tools are
described in the man pages included in the package.
-Project web page: http://nilfs.sourceforge.net/
-Download page: http://nilfs.sourceforge.net/en/download.html
+Project web page: https://nilfs.sourceforge.io/
+Download page: https://nilfs.sourceforge.io/en/download.html
List info: http://vger.kernel.org/vger-lists.html#linux-nilfs
Caveats
diff --git a/Documentation/kbuild/kconfig-language.txt b/Documentation/kbuild/kconfig-language.txt
index 262722d8867b..c4a293a03c33 100644
--- a/Documentation/kbuild/kconfig-language.txt
+++ b/Documentation/kbuild/kconfig-language.txt
@@ -200,10 +200,14 @@ module state. Dependency expressions have the following syntax:
<expr> ::= <symbol> (1)
<symbol> '=' <symbol> (2)
<symbol> '!=' <symbol> (3)
- '(' <expr> ')' (4)
- '!' <expr> (5)
- <expr> '&&' <expr> (6)
- <expr> '||' <expr> (7)
+ <symbol1> '<' <symbol2> (4)
+ <symbol1> '>' <symbol2> (4)
+ <symbol1> '<=' <symbol2> (4)
+ <symbol1> '>=' <symbol2> (4)
+ '(' <expr> ')' (5)
+ '!' <expr> (6)
+ <expr> '&&' <expr> (7)
+ <expr> '||' <expr> (8)
Expressions are listed in decreasing order of precedence.
@@ -214,10 +218,13 @@ Expressions are listed in decreasing order of precedence.
otherwise 'n'.
(3) If the values of both symbols are equal, it returns 'n',
otherwise 'y'.
-(4) Returns the value of the expression. Used to override precedence.
-(5) Returns the result of (2-/expr/).
-(6) Returns the result of min(/expr/, /expr/).
-(7) Returns the result of max(/expr/, /expr/).
+(4) If value of <symbol1> is respectively lower, greater, lower-or-equal,
+ or greater-or-equal than value of <symbol2>, it returns 'y',
+ otherwise 'n'.
+(5) Returns the value of the expression. Used to override precedence.
+(6) Returns the result of (2-/expr/).
+(7) Returns the result of min(/expr/, /expr/).
+(8) Returns the result of max(/expr/, /expr/).
An expression can have a value of 'n', 'm' or 'y' (or 0, 1, 2
respectively for calculations). A menu entry becomes visible when its
diff --git a/Documentation/usb/gadget-testing.txt b/Documentation/usb/gadget-testing.txt
index 441a4b9b666f..5908a21fddb6 100644
--- a/Documentation/usb/gadget-testing.txt
+++ b/Documentation/usb/gadget-testing.txt
@@ -693,7 +693,7 @@ such specification consists of a number of lines with an inverval value
in each line. The rules stated above are best illustrated with an example:
# mkdir functions/uvc.usb0/control/header/h
-# cd functions/uvc.usb0/control/header/h
+# cd functions/uvc.usb0/control/
# ln -s header/h class/fs
# ln -s header/h class/ss
# mkdir -p functions/uvc.usb0/streaming/uncompressed/u/360p
diff --git a/Documentation/x86/pti.txt b/Documentation/x86/pti.txt
new file mode 100644
index 000000000000..d11eff61fc9a
--- /dev/null
+++ b/Documentation/x86/pti.txt
@@ -0,0 +1,186 @@
+Overview
+========
+
+Page Table Isolation (pti, previously known as KAISER[1]) is a
+countermeasure against attacks on the shared user/kernel address
+space such as the "Meltdown" approach[2].
+
+To mitigate this class of attacks, we create an independent set of
+page tables for use only when running userspace applications. When
+the kernel is entered via syscalls, interrupts or exceptions, the
+page tables are switched to the full "kernel" copy. When the system
+switches back to user mode, the user copy is used again.
+
+The userspace page tables contain only a minimal amount of kernel
+data: only what is needed to enter/exit the kernel such as the
+entry/exit functions themselves and the interrupt descriptor table
+(IDT). There are a few strictly unnecessary things that get mapped
+such as the first C function when entering an interrupt (see
+comments in pti.c).
+
+This approach helps to ensure that side-channel attacks leveraging
+the paging structures do not function when PTI is enabled. It can be
+enabled by setting CONFIG_PAGE_TABLE_ISOLATION=y at compile time.
+Once enabled at compile-time, it can be disabled at boot with the
+'nopti' or 'pti=' kernel parameters (see kernel-parameters.txt).
+
+Page Table Management
+=====================
+
+When PTI is enabled, the kernel manages two sets of page tables.
+The first set is very similar to the single set which is present in
+kernels without PTI. This includes a complete mapping of userspace
+that the kernel can use for things like copy_to_user().
+
+Although _complete_, the user portion of the kernel page tables is
+crippled by setting the NX bit in the top level. This ensures
+that any missed kernel->user CR3 switch will immediately crash
+userspace upon executing its first instruction.
+
+The userspace page tables map only the kernel data needed to enter
+and exit the kernel. This data is entirely contained in the 'struct
+cpu_entry_area' structure which is placed in the fixmap which gives
+each CPU's copy of the area a compile-time-fixed virtual address.
+
+For new userspace mappings, the kernel makes the entries in its
+page tables like normal. The only difference is when the kernel
+makes entries in the top (PGD) level. In addition to setting the
+entry in the main kernel PGD, a copy of the entry is made in the
+userspace page tables' PGD.
+
+This sharing at the PGD level also inherently shares all the lower
+layers of the page tables. This leaves a single, shared set of
+userspace page tables to manage. One PTE to lock, one set of
+accessed bits, dirty bits, etc...
+
+Overhead
+========
+
+Protection against side-channel attacks is important. But,
+this protection comes at a cost:
+
+1. Increased Memory Use
+ a. Each process now needs an order-1 PGD instead of order-0.
+ (Consumes an additional 4k per process).
+ b. The 'cpu_entry_area' structure must be 2MB in size and 2MB
+ aligned so that it can be mapped by setting a single PMD
+ entry. This consumes nearly 2MB of RAM once the kernel
+ is decompressed, but no space in the kernel image itself.
+
+2. Runtime Cost
+ a. CR3 manipulation to switch between the page table copies
+ must be done at interrupt, syscall, and exception entry
+ and exit (it can be skipped when the kernel is interrupted,
+ though.) Moves to CR3 are on the order of a hundred
+ cycles, and are required at every entry and exit.
+ b. A "trampoline" must be used for SYSCALL entry. This
+ trampoline depends on a smaller set of resources than the
+ non-PTI SYSCALL entry code, so requires mapping fewer
+ things into the userspace page tables. The downside is
+ that stacks must be switched at entry time.
+ d. Global pages are disabled for all kernel structures not
+ mapped into both kernel and userspace page tables. This
+ feature of the MMU allows different processes to share TLB
+ entries mapping the kernel. Losing the feature means more
+ TLB misses after a context switch. The actual loss of
+ performance is very small, however, never exceeding 1%.
+ d. Process Context IDentifiers (PCID) is a CPU feature that
+ allows us to skip flushing the entire TLB when switching page
+ tables by setting a special bit in CR3 when the page tables
+ are changed. This makes switching the page tables (at context
+ switch, or kernel entry/exit) cheaper. But, on systems with
+ PCID support, the context switch code must flush both the user
+ and kernel entries out of the TLB. The user PCID TLB flush is
+ deferred until the exit to userspace, minimizing the cost.
+ See intel.com/sdm for the gory PCID/INVPCID details.
+ e. The userspace page tables must be populated for each new
+ process. Even without PTI, the shared kernel mappings
+ are created by copying top-level (PGD) entries into each
+ new process. But, with PTI, there are now *two* kernel
+ mappings: one in the kernel page tables that maps everything
+ and one for the entry/exit structures. At fork(), we need to
+ copy both.
+ f. In addition to the fork()-time copying, there must also
+ be an update to the userspace PGD any time a set_pgd() is done
+ on a PGD used to map userspace. This ensures that the kernel
+ and userspace copies always map the same userspace
+ memory.
+ g. On systems without PCID support, each CR3 write flushes
+ the entire TLB. That means that each syscall, interrupt
+ or exception flushes the TLB.
+ h. INVPCID is a TLB-flushing instruction which allows flushing
+ of TLB entries for non-current PCIDs. Some systems support
+ PCIDs, but do not support INVPCID. On these systems, addresses
+ can only be flushed from the TLB for the current PCID. When
+ flushing a kernel address, we need to flush all PCIDs, so a
+ single kernel address flush will require a TLB-flushing CR3
+ write upon the next use of every PCID.
+
+Possible Future Work
+====================
+1. We can be more careful about not actually writing to CR3
+ unless its value is actually changed.
+2. Allow PTI to be enabled/disabled at runtime in addition to the
+ boot-time switching.
+
+Testing
+========
+
+To test stability of PTI, the following test procedure is recommended,
+ideally doing all of these in parallel:
+
+1. Set CONFIG_DEBUG_ENTRY=y
+2. Run several copies of all of the tools/testing/selftests/x86/ tests
+ (excluding MPX and protection_keys) in a loop on multiple CPUs for
+ several minutes. These tests frequently uncover corner cases in the
+ kernel entry code. In general, old kernels might cause these tests
+ themselves to crash, but they should never crash the kernel.
+3. Run the 'perf' tool in a mode (top or record) that generates many
+ frequent performance monitoring non-maskable interrupts (see "NMI"
+ in /proc/interrupts). This exercises the NMI entry/exit code which
+ is known to trigger bugs in code paths that did not expect to be
+ interrupted, including nested NMIs. Using "-c" boosts the rate of
+ NMIs, and using two -c with separate counters encourages nested NMIs
+ and less deterministic behavior.
+
+ while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done
+
+4. Launch a KVM virtual machine.
+5. Run 32-bit binaries on systems supporting the SYSCALL instruction.
+ This has been a lightly-tested code path and needs extra scrutiny.
+
+Debugging
+=========
+
+Bugs in PTI cause a few different signatures of crashes
+that are worth noting here.
+
+ * Failures of the selftests/x86 code. Usually a bug in one of the
+ more obscure corners of entry_64.S
+ * Crashes in early boot, especially around CPU bringup. Bugs
+ in the trampoline code or mappings cause these.
+ * Crashes at the first interrupt. Caused by bugs in entry_64.S,
+ like screwing up a page table switch. Also caused by
+ incorrectly mapping the IRQ handler entry code.
+ * Crashes at the first NMI. The NMI code is separate from main
+ interrupt handlers and can have bugs that do not affect
+ normal interrupts. Also caused by incorrectly mapping NMI
+ code. NMIs that interrupt the entry code must be very
+ careful and can be the cause of crashes that show up when
+ running perf.
+ * Kernel crashes at the first exit to userspace. entry_64.S
+ bugs, or failing to map some of the exit code.
+ * Crashes at first interrupt that interrupts userspace. The paths
+ in entry_64.S that return to userspace are sometimes separate
+ from the ones that return to the kernel.
+ * Double faults: overflowing the kernel stack because of page
+ faults upon page faults. Caused by touching non-pti-mapped
+ data in the entry code, or forgetting to switch to kernel
+ CR3 before calling into C functions which are not pti-mapped.
+ * Userspace segfaults early in boot, sometimes manifesting
+ as mount(8) failing to mount the rootfs. These have
+ tended to be TLB invalidation issues. Usually invalidating
+ the wrong PCID, or otherwise missing an invalidation.
+
+1. https://gruss.cc/files/kaiser.pdf
+2. https://meltdownattack.com/meltdown.pdf