linux-stable.git/tools, branch v5.19.1

x86/speculation: Add RSB VM Exit protections

2022-08-11T11:22:05+00:00

commit 2b1299322016731d56807aa49254a5ea3080b6b3 upstream.

tl;dr: The Enhanced IBRS mitigation for Spectre v2 does not work as
documented for RET instructions after VM exits. Mitigate it with a new
one-entry RSB stuffing mechanism and a new LFENCE.

== Background ==

Indirect Branch Restricted Speculation (IBRS) was designed to help
mitigate Branch Target Injection and Speculative Store Bypass, i.e.
Spectre, attacks. IBRS prevents software run in less privileged modes
from affecting branch prediction in more privileged modes. IBRS requires
the MSR to be written on every privilege level change.

To overcome some of the performance issues of IBRS, Enhanced IBRS was
introduced.  eIBRS is an "always on" IBRS, in other words, just turn
it on once instead of writing the MSR on every privilege level change.
When eIBRS is enabled, more privileged modes should be protected from
less privileged modes, including protecting VMMs from guests.

== Problem ==

Here's a simplification of how guests are run on Linux' KVM:

void run_kvm_guest(void)
{
	// Prepare to run guest
	VMRESUME();
	// Clean up after guest runs
}

The execution flow for that would look something like this to the
processor:

1. Host-side: call run_kvm_guest()
2. Host-side: VMRESUME
3. Guest runs, does "CALL guest_function"
4. VM exit, host runs again
5. Host might make some "cleanup" function calls
6. Host-side: RET from run_kvm_guest()

Now, when back on the host, there are a couple of possible scenarios of
post-guest activity the host needs to do before executing host code:

* on pre-eIBRS hardware (legacy IBRS, or nothing at all), the RSB is not
touched and Linux has to do a 32-entry stuffing.

* on eIBRS hardware, VM exit with IBRS enabled, or restoring the host
IBRS=1 shortly after VM exit, has a documented side effect of flushing
the RSB except in this PBRSB situation where the software needs to stuff
the last RSB entry "by hand".

IOW, with eIBRS supported, host RET instructions should no longer be
influenced by guest behavior after the host retires a single CALL
instruction.

However, if the RET instructions are "unbalanced" with CALLs after a VM
exit as is the RET in #6, it might speculatively use the address for the
instruction after the CALL in #3 as an RSB prediction. This is a problem
since the (untrusted) guest controls this address.

Balanced CALL/RET instruction pairs such as in step #5 are not affected.

== Solution ==

The PBRSB issue affects a wide variety of Intel processors which
support eIBRS. But not all of them need mitigation. Today,
X86_FEATURE_RSB_VMEXIT triggers an RSB filling sequence that mitigates
PBRSB. Systems setting RSB_VMEXIT need no further mitigation - i.e.,
eIBRS systems which enable legacy IBRS explicitly.

However, such systems (X86_FEATURE_IBRS_ENHANCED) do not set RSB_VMEXIT
and most of them need a new mitigation.

Therefore, introduce a new feature flag X86_FEATURE_RSB_VMEXIT_LITE
which triggers a lighter-weight PBRSB mitigation versus RSB_VMEXIT.

The lighter-weight mitigation performs a CALL instruction which is
immediately followed by a speculative execution barrier (INT3). This
steers speculative execution to the barrier -- just like a retpoline
-- which ensures that speculation can never reach an unbalanced RET.
Then, ensure this CALL is retired before continuing execution with an
LFENCE.

In other words, the window of exposure is opened at VM exit where RET
behavior is troublesome. While the window is open, force RSB predictions
sampling for RET targets to a dead end at the INT3. Close the window
with the LFENCE.

There is a subset of eIBRS systems which are not vulnerable to PBRSB.
Add these systems to the cpu_vuln_whitelist[] as NO_EIBRS_PBRSB.
Future systems that aren't vulnerable will set ARCH_CAP_PBRSB_NO.

  [ bp: Massage, incorporate review comments from Andy Cooper. ]

Signed-off-by: Daniel Sneddon 
Co-developed-by: Pawan Gupta 
Signed-off-by: Pawan Gupta 
Signed-off-by: Borislav Petkov 
Signed-off-by: Greg Kroah-Hartman

tools/vm/slabinfo: Handle files in debugfs

2022-08-11T11:22:02+00:00

commit 0c7e0d699ef1430d7f4cf12b4b1d097af58b5515 upstream.

Commit 64dd68497be76 relocated and renamed the alloc_calls and
free_calls files from /sys/kernel/slab/NAME/*_calls over to
/sys/kernel/debug/slab/NAME/*_calls but didn't update the slabinfo tool
with the new location.

This change will now have slabinfo look at the new location (and filenames)
with a fallback to the prior files.

Fixes: 64dd68497be76 ("mm: slub: move sysfs slab alloc/free interfaces to debugfs")
Cc: stable@vger.kernel.org
Signed-off-by: Stéphane Graber 
Tested-by: Stéphane Graber 
Signed-off-by: Vlastimil Babka 
Signed-off-by: Greg Kroah-Hartman

Merge tag 'perf-tools-fixes-for-v5.19-2022-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux

2022-07-29T18:26:28+00:00

Pull perf tools fixes from Arnaldo Carvalho de Melo:

 - Fix addresses for bss symbols, describing variables used in resolving
   data access in tools such as 'perf c2c' and 'perf mem'.

 - Skip symbols if SHF_ALLOC flag is not set, a technique used for
   listing deprecated symbols, its addresses are zeros, so not useful.

 - Remove undefined behavior from bpf_perf_object__next() when dealing
   with an empty bpf_objects_list list.

 - Make a ARM CoreSight disasm script work with both python2 and
   python3.

 - Sync x86's cpufeatures header with with the kernel sources.

* tag 'perf-tools-fixes-for-v5.19-2022-07-29' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux:
  perf bpf: Remove undefined behavior from bpf_perf_object__next()
  perf symbol: Skip symbols if SHF_ALLOC flag is not set
  perf symbol: Correct address for bss symbols
  perf scripts python: Let script to be python2 compliant
  tools headers cpufeatures: Sync with the kernel sources

Merge tag 'asm-generic-fixes-5.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic

2022-07-27T16:50:18+00:00

Pull asm-generic fixes from Arnd Bergmann:
 "Two more bug fixes for asm-generic, one addressing an incorrect
  Kconfig symbol reference and another one fixing a build failure for
  the perf tool on mips and possibly others"

* tag 'asm-generic-fixes-5.19-2' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
  asm-generic: remove a broken and needless ifdef conditional
  tools: Fixed MIPS builds due to struct flock re-definition

perf bpf: Remove undefined behavior from bpf_perf_object__next()

2022-07-27T14:19:39+00:00

bpf_perf_object__next() folded the last element in the list test with the
empty list test. However, this meant that offsets were computed against
null and that a struct list_head was compared against a 'struct
bpf_perf_object'.

Working around this with clang's undefined behavior sanitizer required
-fno-sanitize=null and -fno-sanitize=object-size.

Remove the undefined behavior by using the regular Linux list APIs and
handling the starting case separately from the end testing case.

Looking at uses like bpf_perf_object__for_each(), as the constant NULL
or non-NULL argument can be constant propagated, the code is no less
efficient.

Signed-off-by: Ian Rogers 
Cc: Alexander Shishkin 
Cc: Alexei Starovoitov 
Cc: Andrii Nakryiko 
Cc: Christy Lee 
Cc: Ingo Molnar 
Cc: Jiri Olsa 
Cc: Mark Rutland 
Cc: Miaoqian Lin 
Cc: Namhyung Kim 
Cc: Nathan Chancellor 
Cc: Nick Desaulniers 
Cc: Peter Zijlstra 
Cc: Stephane Eranian 
Cc: Tom Rix 
Cc: bpf@vger.kernel.org
Cc: llvm@lists.linux.dev
Link: https://lore.kernel.org/r/20220726220921.2567761-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo

perf symbol: Skip symbols if SHF_ALLOC flag is not set

2022-07-27T14:17:50+00:00

Some symbols are observed with the 'st_value' field zeroed.  E.g.
libc.so.6 in Ubuntu contains a symbol '__evoke_link_warning_getwd' which
resides in the '.gnu.warning.getwd' section.

Unlike normal sections, such kind of sections are used for linker
warning when a file calls deprecated functions, but they are not part of
memory images, the symbols in these sections should be dropped.

This patch checks the section attribute SHF_ALLOC bit, if the bit is not
set, it skips symbols to avoid spurious ones.

Suggested-by: Fangrui Song 
Signed-off-by: Leo Yan 
Acked-by: Namhyung Kim 
Cc: Alexander Shishkin 
Cc: Chang Rui 
Cc: Ian Rogers 
Cc: Ingo Molnar 
Cc: Jiri Olsa 
Cc: Mark Rutland 
Cc: Peter Zijlstra 
Link: https://lore.kernel.org/r/20220724060013.171050-3-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo

perf symbol: Correct address for bss symbols

2022-07-27T14:17:50+00:00

When using 'perf mem' and 'perf c2c', an issue is observed that tool
reports the wrong offset for global data symbols.  This is a common
issue on both x86 and Arm64 platforms.

Let's see an example, for a test program, below is the disassembly for
its .bss section which is dumped with objdump:

  ...

  Disassembly of section .bss:

  0000000000004040 :
  	...

  0000000000004080 :
  	...

  00000000000040c0 :
  	...

  0000000000004100 :
  	...

First we used 'perf mem record' to run the test program and then used
'perf --debug verbose=4 mem report' to observe what's the symbol info
for 'buf1' and 'buf2' structures.

  # ./perf mem record -e ldlat-loads,ldlat-stores -- false_sharing.exe 8
  # ./perf --debug verbose=4 mem report
    ...
    dso__load_sym_internal: adjusting symbol: st_value: 0x40c0 sh_addr: 0x4040 sh_offset: 0x3028
    symbol__new: buf2 0x30a8-0x30e8
    ...
    dso__load_sym_internal: adjusting symbol: st_value: 0x4080 sh_addr: 0x4040 sh_offset: 0x3028
    symbol__new: buf1 0x3068-0x30a8
    ...

The perf tool relies on libelf to parse symbols, in executable and
shared object files, 'st_value' holds a virtual address; 'sh_addr' is
the address at which section's first byte should reside in memory, and
'sh_offset' is the byte offset from the beginning of the file to the
first byte in the section.  The perf tool uses below formula to convert
a symbol's memory address to a file address:

  file_address = st_value - sh_addr + sh_offset
                    ^
                    ` Memory address

We can see the final adjusted address ranges for buf1 and buf2 are
[0x30a8-0x30e8) and [0x3068-0x30a8) respectively, apparently this is
incorrect, in the code, the structure for 'buf1' and 'buf2' specifies
compiler attribute with 64-byte alignment.

The problem happens for 'sh_offset', libelf returns it as 0x3028 which
is not 64-byte aligned, combining with disassembly, it's likely libelf
doesn't respect the alignment for .bss section, therefore, it doesn't
return the aligned value for 'sh_offset'.

Suggested by Fangrui Song, ELF file contains program header which
contains PT_LOAD segments, the fields p_vaddr and p_offset in PT_LOAD
segments contain the execution info.  A better choice for converting
memory address to file address is using the formula:

  file_address = st_value - p_vaddr + p_offset

This patch introduces elf_read_program_header() which returns the
program header based on the passed 'st_value', then it uses the formula
above to calculate the symbol file address; and the debugging log is
updated respectively.

After applying the change:

  # ./perf --debug verbose=4 mem report
    ...
    dso__load_sym_internal: adjusting symbol: st_value: 0x40c0 p_vaddr: 0x3d28 p_offset: 0x2d28
    symbol__new: buf2 0x30c0-0x3100
    ...
    dso__load_sym_internal: adjusting symbol: st_value: 0x4080 p_vaddr: 0x3d28 p_offset: 0x2d28
    symbol__new: buf1 0x3080-0x30c0
    ...

Fixes: f17e04afaff84b5c ("perf report: Fix ELF symbol parsing")
Reported-by: Chang Rui 
Suggested-by: Fangrui Song 
Signed-off-by: Leo Yan 
Acked-by: Namhyung Kim 
Cc: Alexander Shishkin 
Cc: Ian Rogers 
Cc: Ingo Molnar 
Cc: Jiri Olsa 
Cc: Mark Rutland 
Cc: Peter Zijlstra 
Link: https://lore.kernel.org/r/20220724060013.171050-2-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo

perf scripts python: Let script to be python2 compliant

2022-07-27T14:17:50+00:00

The mainline kernel can be used for relative old distros, e.g. RHEL 7.
The distro doesn't upgrade from python2 to python3, this causes the
building error that the python script is not python2 compliant.

To fix the building failure, this patch changes from the python f-string
format to traditional string format.

Fixes: 12fdd6c009da0d02 ("perf scripts python: Support Arm CoreSight trace data disassembly")
Reported-by: Akemi Yagi 
Signed-off-by: Leo Yan 
Cc: Alexander Shishkin 
Cc: ElRepo 
Cc: Ian Rogers 
Cc: Ingo Molnar 
Cc: Jiri Olsa 
Cc: Leo Yan 
Cc: Mark Rutland 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Link: https://lore.kernel.org/r/20220725104220.1106663-1-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo

tools headers cpufeatures: Sync with the kernel sources

2022-07-27T14:17:50+00:00

To pick the changes from:

  28a99e95f55c6185 ("x86/amd: Use IBPB for firmware calls")

This only causes these perf files to be rebuilt:

  CC       /tmp/build/perf/bench/mem-memcpy-x86-64-asm.o
  CC       /tmp/build/perf/bench/mem-memset-x86-64-asm.o

And addresses this perf build warning:

  Warning: Kernel ABI header at 'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version at 'arch/x86/include/asm/cpufeatures.h'
  diff -u tools/arch/x86/include/asm/cpufeatures.h arch/x86/include/asm/cpufeatures.h

Cc: Adrian Hunter 
Cc: Borislav Petkov 
Cc: Ian Rogers 
Cc: Jiri Olsa 
Cc: Namhyung Kim 
Cc: Peter Zijlstra

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2022-07-23T17:22:26+00:00

Pull kvm fixes from Paolo Bonzini:

 - Check for invalid flags to KVM_CAP_X86_USER_SPACE_MSR

 - Fix use of sched_setaffinity in selftests

 - Sync kernel headers to tools

 - Fix KVM_STATS_UNIT_MAX

* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: x86: Protect the unused bits in MSR exiting flags
  tools headers UAPI: Sync linux/kvm.h with the kernel sources
  KVM: selftests: Fix target thread to be migrated in rseq_test
  KVM: stats: Fix value for KVM_STATS_UNIT_MAX for boolean stats