linux-stable.git/Documentation/admin-guide/kernel-parameters.txt, branch v4.19.78

x86/CPU/AMD: Clear RDRAND CPUID bit on AMD family 15h/16h

2019-08-29T06:28:53+00:00

commit c49a0a80137c7ca7d6ced4c812c9e07a949f6f24 upstream.

There have been reports of RDRAND issues after resuming from suspend on
some AMD family 15h and family 16h systems. This issue stems from a BIOS
not performing the proper steps during resume to ensure RDRAND continues
to function properly.

RDRAND support is indicated by CPUID Fn00000001_ECX[30]. This bit can be
reset by clearing MSR C001_1004[62]. Any software that checks for RDRAND
support using CPUID, including the kernel, will believe that RDRAND is
not supported.

Update the CPU initialization to clear the RDRAND CPUID bit for any family
15h and 16h processor that supports RDRAND. If it is known that the family
15h or family 16h system does not have an RDRAND resume issue or that the
system will not be placed in suspend, the "rdrand=force" kernel parameter
can be used to stop the clearing of the RDRAND CPUID bit.

Additionally, update the suspend and resume path to save and restore the
MSR C001_1004 value to ensure that the RDRAND CPUID setting remains in
place after resuming from suspend.

Note, that clearing the RDRAND CPUID bit does not prevent a processor
that normally supports the RDRAND instruction from executing it. So any
code that determined the support based on family and model won't #UD.

Signed-off-by: Tom Lendacky 
Signed-off-by: Borislav Petkov 
Cc: Andrew Cooper 
Cc: Andrew Morton 
Cc: Chen Yu 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jonathan Corbet 
Cc: Josh Poimboeuf 
Cc: Juergen Gross 
Cc: Kees Cook 
Cc: "linux-doc@vger.kernel.org" 
Cc: "linux-pm@vger.kernel.org" 
Cc: Nathan Chancellor 
Cc: Paolo Bonzini 
Cc: Pavel Machek 
Cc: "Rafael J. Wysocki" 
Cc: 
Cc: Thomas Gleixner 
Cc: "x86@kernel.org" 
Link: https://lkml.kernel.org/r/7543af91666f491547bd86cebb1e17c66824ab9f.1566229943.git.thomas.lendacky@amd.com
Signed-off-by: Greg Kroah-Hartman

x86/speculation: Enable Spectre v1 swapgs mitigations

2019-08-06T17:06:58+00:00

commit a2059825986a1c8143fd6698774fa9d83733bb11 upstream

The previous commit added macro calls in the entry code which mitigate the
Spectre v1 swapgs issue if the X86_FEATURE_FENCE_SWAPGS_* features are
enabled.  Enable those features where applicable.

The mitigations may be disabled with "nospectre_v1" or "mitigations=off".

There are different features which can affect the risk of attack:

- When FSGSBASE is enabled, unprivileged users are able to place any
  value in GS, using the wrgsbase instruction.  This means they can
  write a GS value which points to any value in kernel space, which can
  be useful with the following gadget in an interrupt/exception/NMI
  handler:

	if (coming from user space)
		swapgs
	mov %gs:, %reg1
	// dependent load or store based on the value of %reg
	// for example: mov %(reg1), %reg2

  If an interrupt is coming from user space, and the entry code
  speculatively skips the swapgs (due to user branch mistraining), it
  may speculatively execute the GS-based load and a subsequent dependent
  load or store, exposing the kernel data to an L1 side channel leak.

  Note that, on Intel, a similar attack exists in the above gadget when
  coming from kernel space, if the swapgs gets speculatively executed to
  switch back to the user GS.  On AMD, this variant isn't possible
  because swapgs is serializing with respect to future GS-based
  accesses.

  NOTE: The FSGSBASE patch set hasn't been merged yet, so the above case
	doesn't exist quite yet.

- When FSGSBASE is disabled, the issue is mitigated somewhat because
  unprivileged users must use prctl(ARCH_SET_GS) to set GS, which
  restricts GS values to user space addresses only.  That means the
  gadget would need an additional step, since the target kernel address
  needs to be read from user space first.  Something like:

	if (coming from user space)
		swapgs
	mov %gs:, %reg1
	mov (%reg1), %reg2
	// dependent load or store based on the value of %reg2
	// for example: mov %(reg2), %reg3

  It's difficult to audit for this gadget in all the handlers, so while
  there are no known instances of it, it's entirely possible that it
  exists somewhere (or could be introduced in the future).  Without
  tooling to analyze all such code paths, consider it vulnerable.

  Effects of SMAP on the !FSGSBASE case:

  - If SMAP is enabled, and the CPU reports RDCL_NO (i.e., not
    susceptible to Meltdown), the kernel is prevented from speculatively
    reading user space memory, even L1 cached values.  This effectively
    disables the !FSGSBASE attack vector.

  - If SMAP is enabled, but the CPU *is* susceptible to Meltdown, SMAP
    still prevents the kernel from speculatively reading user space
    memory.  But it does *not* prevent the kernel from reading the
    user value from L1, if it has already been cached.  This is probably
    only a small hurdle for an attacker to overcome.

Thanks to Dave Hansen for contributing the speculative_smap() function.

Thanks to Andrew Cooper for providing the inside scoop on whether swapgs
is serializing on AMD.

[ tglx: Fixed the USER fence decision and polished the comment as suggested
  	by Dave Hansen ]

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Dave Hansen 
Signed-off-by: Greg Kroah-Hartman

Documentation/admin: Remove the vsyscall=native documentation

2019-07-14T06:11:18+00:00

commit d974ffcfb7447db5f29a4b662a3eaf99a4e1109e upstream.

The vsyscall=native feature is gone -- remove the docs.

Fixes: 076ca272a14c ("x86/vsyscall/64: Drop "native" vsyscalls")
Signed-off-by: Andy Lutomirski 
Signed-off-by: Thomas Gleixner 
Acked-by: Kees Cook 
Cc: Florian Weimer 
Cc: Jann Horn 
Cc: stable@vger.kernel.org
Cc: Borislav Petkov 
Cc: Kernel Hardening 
Cc: Peter Zijlstra 
Link: https://lkml.kernel.org/r/d77c7105eb4c57c1a95a95b6a5b8ba194a18e764.1561610354.git.luto@kernel.org
Signed-off-by: Greg Kroah-Hartman

x86/speculation/mds: Add 'mitigations=' support for MDS

2019-05-14T17:17:59+00:00

commit 5c14068f87d04adc73ba3f41c2a303d3c3d1fa12 upstream

Add MDS to the new 'mitigations=' cmdline option.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

s390/speculation: Support 'mitigations=' cmdline option

2019-05-14T17:17:59+00:00

commit 0336e04a6520bdaefdb0769d2a70084fa52e81ed upstream

Configure s390 runtime CPU speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Spectre v1 and
Spectre v2.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina  (on x86)
Reviewed-by: Jiri Kosina 
Cc: Borislav Petkov 
Cc: "H . Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Peter Zijlstra 
Cc: Jiri Kosina 
Cc: Waiman Long 
Cc: Andrea Arcangeli 
Cc: Jon Masters 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas 
Cc: Will Deacon 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Tyler Hicks 
Cc: Linus Torvalds 
Cc: Randy Dunlap 
Cc: Steven Price 
Cc: Phil Auld 
Link: https://lkml.kernel.org/r/e4a161805458a5ec88812aac0307ae3908a030fc.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman

powerpc/speculation: Support 'mitigations=' cmdline option

2019-05-14T17:17:59+00:00

commit 782e69efb3dfed6e8360bc612e8c7827a901a8f9 upstream

Configure powerpc CPU runtime speculation bug mitigations in accordance
with the 'mitigations=' cmdline option.  This affects Meltdown, Spectre
v1, Spectre v2, and Speculative Store Bypass.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina  (on x86)
Reviewed-by: Jiri Kosina 
Cc: Borislav Petkov 
Cc: "H . Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Peter Zijlstra 
Cc: Jiri Kosina 
Cc: Waiman Long 
Cc: Andrea Arcangeli 
Cc: Jon Masters 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas 
Cc: Will Deacon 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Tyler Hicks 
Cc: Linus Torvalds 
Cc: Randy Dunlap 
Cc: Steven Price 
Cc: Phil Auld 
Link: https://lkml.kernel.org/r/245a606e1a42a558a310220312d9b6adb9159df6.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman

x86/speculation: Support 'mitigations=' cmdline option

2019-05-14T17:17:59+00:00

commit d68be4c4d31295ff6ae34a8ddfaa4c1a8ff42812 upstream

Configure x86 runtime CPU speculation bug mitigations in accordance with
the 'mitigations=' cmdline option.  This affects Meltdown, Spectre v2,
Speculative Store Bypass, and L1TF.

The default behavior is unchanged.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina  (on x86)
Reviewed-by: Jiri Kosina 
Cc: Borislav Petkov 
Cc: "H . Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Peter Zijlstra 
Cc: Jiri Kosina 
Cc: Waiman Long 
Cc: Andrea Arcangeli 
Cc: Jon Masters 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas 
Cc: Will Deacon 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Tyler Hicks 
Cc: Linus Torvalds 
Cc: Randy Dunlap 
Cc: Steven Price 
Cc: Phil Auld 
Link: https://lkml.kernel.org/r/6616d0ae169308516cfdf5216bedd169f8a8291b.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman

cpu/speculation: Add 'mitigations=' cmdline option

2019-05-14T17:17:59+00:00

commit 98af8452945c55652de68536afdde3b520fec429 upstream

Keeping track of the number of mitigations for all the CPU speculation
bugs has become overwhelming for many users.  It's getting more and more
complicated to decide which mitigations are needed for a given
architecture.  Complicating matters is the fact that each arch tends to
have its own custom way to mitigate the same vulnerability.

Most users fall into a few basic categories:

a) they want all mitigations off;

b) they want all reasonable mitigations on, with SMT enabled even if
   it's vulnerable; or

c) they want all reasonable mitigations on, with SMT disabled if
   vulnerable.

Define a set of curated, arch-independent options, each of which is an
aggregation of existing options:

- mitigations=off: Disable all mitigations.

- mitigations=auto: [default] Enable all the default mitigations, but
  leave SMT enabled, even if it's vulnerable.

- mitigations=auto,nosmt: Enable all the default mitigations, disabling
  SMT if needed by a mitigation.

Currently, these options are placeholders which don't actually do
anything.  They will be fleshed out in upcoming patches.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Tested-by: Jiri Kosina  (on x86)
Reviewed-by: Jiri Kosina 
Cc: Borislav Petkov 
Cc: "H . Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Peter Zijlstra 
Cc: Jiri Kosina 
Cc: Waiman Long 
Cc: Andrea Arcangeli 
Cc: Jon Masters 
Cc: Benjamin Herrenschmidt 
Cc: Paul Mackerras 
Cc: Michael Ellerman 
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Martin Schwidefsky 
Cc: Heiko Carstens 
Cc: linux-s390@vger.kernel.org
Cc: Catalin Marinas 
Cc: Will Deacon 
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org
Cc: Greg Kroah-Hartman 
Cc: Tyler Hicks 
Cc: Linus Torvalds 
Cc: Randy Dunlap 
Cc: Steven Price 
Cc: Phil Auld 
Link: https://lkml.kernel.org/r/b07a8ef9b7c5055c3a4637c87d07c296d5016fe0.1555085500.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman

x86/speculation/mds: Add mds=full,nosmt cmdline option

2019-05-14T17:17:58+00:00

commit d71eb0ce109a124b0fa714832823b9452f2762cf upstream

Add the mds=full,nosmt cmdline option.  This is like mds=full, but with
SMT disabled if the CPU is vulnerable.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Tyler Hicks 
Acked-by: Jiri Kosina 
Signed-off-by: Greg Kroah-Hartman

Documentation: Add MDS vulnerability documentation

2019-05-14T17:17:58+00:00

commit 5999bbe7a6ea3c62029532ec84dc06003a1fa258 upstream

Add the initial MDS vulnerability documentation.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Jon Masters 
Signed-off-by: Greg Kroah-Hartman