linux.git/arch/x86/kernel/cpu, branch v5.17

Merge tag 'x86_urgent_for_v5.17_rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-03-13T17:36:38+00:00

Pull x86 fixes from Borislav Petkov:

 - Free shmem backing storage for SGX enclave pages when those are
   swapped back into EPC memory

 - Prevent do_int3() from being kprobed, to avoid recursion

 - Remap setup_data and setup_indirect structures properly when
   accessing their members

 - Correct the alternatives patching order for modules too

* tag 'x86_urgent_for_v5.17_rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/sgx: Free backing memory after faulting the enclave page
  x86/traps: Mark do_int3() NOKPROBE_SYMBOL
  x86/boot: Add setup_indirect support in early_memremap_is_setup_data()
  x86/boot: Fix memremap of setup_indirect structures
  x86/module: Fix the paravirt vs alternative order

x86/sgx: Free backing memory after faulting the enclave page

2022-03-11T18:31:06+00:00

There is a limited amount of SGX memory (EPC) on each system.  When that
memory is used up, SGX has its own swapping mechanism which is similar
in concept but totally separate from the core mm/* code.  Instead of
swapping to disk, SGX swaps from EPC to normal RAM.  That normal RAM
comes from a shared memory pseudo-file and can itself be swapped by the
core mm code.  There is a hierarchy like this:

	EPC <-> shmem <-> disk

After data is swapped back in from shmem to EPC, the shmem backing
storage needs to be freed.  Currently, the backing shmem is not freed.
This effectively wastes the shmem while the enclave is running.  The
memory is recovered when the enclave is destroyed and the backing
storage freed.

Sort this out by freeing memory with shmem_truncate_range(), as soon as
a page is faulted back to the EPC.  In addition, free the memory for
PCMD pages as soon as all PCMD's in a page have been marked as unused
by zeroing its contents.

Cc: stable@vger.kernel.org
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
Reported-by: Dave Hansen 
Signed-off-by: Jarkko Sakkinen 
Signed-off-by: Dave Hansen 
Link: https://lkml.kernel.org/r/20220303223859.273187-1-jarkko@kernel.org

x86/speculation: Warn about eIBRS + LFENCE + Unprivileged eBPF + SMT

2022-03-05T08:30:47+00:00

The commit

   44a3918c8245 ("x86/speculation: Include unprivileged eBPF status in Spectre v2 mitigation reporting")

added a warning for the "eIBRS + unprivileged eBPF" combination, which
has been shown to be vulnerable against Spectre v2 BHB-based attacks.

However, there's no warning about the "eIBRS + LFENCE retpoline +
unprivileged eBPF" combo. The LFENCE adds more protection by shortening
the speculation window after a mispredicted branch. That makes an attack
significantly more difficult, even with unprivileged eBPF. So at least
for now the logic doesn't warn about that combination.

But if you then add SMT into the mix, the SMT attack angle weakens the
effectiveness of the LFENCE considerably.

So extend the "eIBRS + unprivileged eBPF" warning to also include the
"eIBRS + LFENCE + unprivileged eBPF + SMT" case.

  [ bp: Massage commit message. ]

Suggested-by: Alyssa Milburn 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86/speculation: Warn about Spectre v2 LFENCE mitigation

2022-03-05T08:16:24+00:00

With:

  f8a66d608a3e ("x86,bugs: Unconditionally allow spectre_v2=retpoline,amd")

it became possible to enable the LFENCE "retpoline" on Intel. However,
Intel doesn't recommend it, as it has some weaknesses compared to
retpoline.

Now AMD doesn't recommend it either.

It can still be left available as a cmdline option. It's faster than
retpoline but is weaker in certain scenarios -- particularly SMT, but
even non-SMT may be vulnerable in some cases.

So just unconditionally warn if the user requests it on the cmdline.

  [ bp: Massage commit message. ]

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86/speculation: Use generic retpoline by default on AMD

2022-02-28T17:37:08+00:00

AMD retpoline may be susceptible to speculation. The speculation
execution window for an incorrect indirect branch prediction using
LFENCE/JMP sequence may potentially be large enough to allow
exploitation using Spectre V2.

By default, don't use retpoline,lfence on AMD.  Instead, use the
generic retpoline.

Signed-off-by: Kim Phillips 
Signed-off-by: Borislav Petkov

x86/speculation: Include unprivileged eBPF status in Spectre v2 mitigation reporting

2022-02-21T09:21:47+00:00

With unprivileged eBPF enabled, eIBRS (without retpoline) is vulnerable
to Spectre v2 BHB-based attacks.

When both are enabled, print a warning message and report it in the
'spectre_v2' sysfs vulnerabilities file.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov 
Reviewed-by: Thomas Gleixner

x86/speculation: Add eIBRS + Retpoline options

2022-02-21T09:21:35+00:00

Thanks to the chaps at VUsec it is now clear that eIBRS is not
sufficient, therefore allow enabling of retpolines along with eIBRS.

Add spectre_v2=eibrs, spectre_v2=eibrs,lfence and
spectre_v2=eibrs,retpoline options to explicitly pick your preferred
means of mitigation.

Since there's new mitigations there's also user visible changes in
/sys/devices/system/cpu/vulnerabilities/spectre_v2 to reflect these
new mitigations.

  [ bp: Massage commit message, trim error messages,
    do more precise eIBRS mode checking. ]

Co-developed-by: Josh Poimboeuf 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Patrick Colp 
Reviewed-by: Thomas Gleixner

x86/speculation: Rename RETPOLINE_AMD to RETPOLINE_LFENCE

2022-02-21T09:21:28+00:00

The RETPOLINE_AMD name is unfortunate since it isn't necessarily
AMD only, in fact Hygon also uses it. Furthermore it will likely be
sufficient for some Intel processors. Therefore rename the thing to
RETPOLINE_LFENCE to better describe what it is.

Add the spectre_v2=retpoline,lfence option as an alias to
spectre_v2=retpoline,amd to preserve existing setups. However, the output
of /sys/devices/system/cpu/vulnerabilities/spectre_v2 will be changed.

  [ bp: Fix typos, massage. ]

Co-developed-by: Josh Poimboeuf 
Signed-off-by: Josh Poimboeuf 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Thomas Gleixner

x86/sgx: Fix missing poison handling in reclaimer

2022-02-17T18:24:50+00:00

The SGX reclaimer code lacks page poison handling in its main
free path. This can lead to avoidable machine checks if a
poisoned page is freed and reallocated instead of being
isolated.

A troublesome scenario is:
 1. Machine check (#MC) occurs (asynchronous, !MF_ACTION_REQUIRED)
 2. arch_memory_failure() is eventually called
 3. (SGX) page->poison set to 1
 4. Page is reclaimed
 5. Page added to normal free lists by sgx_reclaim_pages()
    ^ This is the bug (poison pages should be isolated on the
    sgx_poison_page_list instead)
 6. Page is reallocated by some innocent enclave, a second (synchronous)
    in-kernel #MC is induced, probably during EADD instruction.
    ^ This is the fallout from the bug

(6) is unfortunate and can be avoided by replacing the open coded
enclave page freeing code in the reclaimer with sgx_free_epc_page()
to obtain support for poison page handling that includes placing the
poisoned page on the correct list.

Fixes: d6d261bded8a ("x86/sgx: Add new sgx_epc_page flag bit to mark free pages")
Fixes: 992801ae9243 ("x86/sgx: Initial poison handling for dirty and free pages")
Signed-off-by: Reinette Chatre 
Signed-off-by: Dave Hansen 
Reviewed-by: Jarkko Sakkinen 
Link: https://lkml.kernel.org/r/dcc95eb2aaefb042527ac50d0a50738c7c160dac.1643830353.git.reinette.chatre@intel.com

x86/sgx: Silence softlockup detection when releasing large enclaves

2022-02-10T23:58:14+00:00

Vijay reported that the "unclobbered_vdso_oversubscribed" selftest
triggers the softlockup detector.

Actual SGX systems have 128GB of enclave memory or more.  The
"unclobbered_vdso_oversubscribed" selftest creates one enclave which
consumes all of the enclave memory on the system. Tearing down such a
large enclave takes around a minute, most of it in the loop where
the EREMOVE instruction is applied to each individual 4k enclave page.

Spending one minute in a loop triggers the softlockup detector.

Add a cond_resched() to give other tasks a chance to run and placate
the softlockup detector.

Cc: stable@vger.kernel.org
Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
Reported-by: Vijay Dhanraj 
Signed-off-by: Reinette Chatre 
Signed-off-by: Dave Hansen 
Reviewed-by: Jarkko Sakkinen 
Acked-by: Dave Hansen 
Tested-by: Jarkko Sakkinen   (kselftest as sanity check)
Link: https://lkml.kernel.org/r/ced01cac1e75f900251b0a4ae1150aa8ebd295ec.1644345232.git.reinette.chatre@intel.com