linux-stable.git/arch/x86/kernel/vmlinux.lds.S, branch v6.2

x86/ibt: Implement FineIBT

2022-11-01T12:44:10+00:00

Implement an alternative CFI scheme that merges both the fine-grained
nature of kCFI but also takes full advantage of the coarse grained
hardware CFI as provided by IBT.

To contrast:

  kCFI is a pure software CFI scheme and relies on being able to read
text -- specifically the instruction *before* the target symbol, and
does the hash validation *before* doing the call (otherwise control
flow is compromised already).

  FineIBT is a software and hardware hybrid scheme; by ensuring every
branch target starts with a hash validation it is possible to place
the hash validation after the branch. This has several advantages:

   o the (hash) load is avoided; no memop; no RX requirement.

   o IBT WAIT-FOR-ENDBR state is a speculation stop; by placing
     the hash validation in the immediate instruction after
     the branch target there is a minimal speculation window
     and the whole is a viable defence against SpectreBHB.

   o Kees feels obliged to mention it is slightly more vulnerable
     when the attacker can write code.

Obviously this patch relies on kCFI, but additionally it also relies
on the padding from the call-depth-tracking patches. It uses this
padding to place the hash-validation while the call-sites are
re-written to modify the indirect target to be 16 bytes in front of
the original target, thus hitting this new preamble.

Notably, there is no hardware that needs call-depth-tracking (Skylake)
and supports IBT (Tigerlake and onwards).

Suggested-by: Joao Moreira (Intel) 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Kees Cook 
Link: https://lore.kernel.org/r/20221027092842.634714496@infradead.org

x86/callthunks: Add call patching for call depth tracking

2022-10-17T14:41:13+00:00

Mitigating the Intel SKL RSB underflow issue in software requires to
track the call depth. That is every CALL and every RET need to be
intercepted and additional code injected.

The existing retbleed mitigations already include means of redirecting
RET to __x86_return_thunk; this can be re-purposed and RET can be
redirected to another function doing RET accounting.

CALL accounting will use the function padding introduced in prior
patches. For each CALL instruction, the destination symbol's padding
is rewritten to do the accounting and the CALL instruction is adjusted
to call into the padding.

This ensures only affected CPUs pay the overhead of this accounting.
Unaffected CPUs will leave the padding unused and have their 'JMP
__x86_return_thunk' replaced with an actual 'RET' instruction.

Objtool has been modified to supply a .call_sites section that lists
all the 'CALL' instructions. Additionally the paravirt instruction
sites are iterated since they will have been patched from an indirect
call to direct calls (or direct instructions in which case it'll be
ignored).

Module handling and the actual thunk code for SKL will be added in
subsequent steps.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111147.470877038@infradead.org

objtool: Add .call_sites section

2022-10-17T14:41:07+00:00

In preparation for call depth tracking provide a section which collects all
direct calls.

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111146.016511961@infradead.org

x86: Sanitize linker script

2022-10-17T14:40:57+00:00

The section ordering in the text section is more than suboptimal:

    ALIGN_ENTRY_TEXT_BEGIN
    ENTRY_TEXT
    ALIGN_ENTRY_TEXT_END
    SOFTIRQENTRY_TEXT
    STATIC_CALL_TEXT
    INDIRECT_THUNK_TEXT

ENTRY_TEXT is in a seperate PMD so it can be mapped into the cpu entry area
when KPTI is enabled. That means the sections after it are also in a
seperate PMD. That's wasteful especially as the indirect thunk text is a
hotpath on retpoline enabled systems and the static call text is fairly hot
on 32bit.

Move the entry text section last so that the other sections share a PMD
with the text before it. This is obviously just best effort and not
guaranteed when the previous text is just at a PMD boundary.

The text section placement needs an overhaul in general. There is e.g. no
point to have debugfs, sysfs, cpuhotplug and other rarely used functions
next to hot path text.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20220915111143.614728935@infradead.org

Merge tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2022-07-12T01:15:25+00:00

Pull x86 retbleed fixes from Borislav Petkov:
 "Just when you thought that all the speculation bugs were addressed and
  solved and the nightmare is complete, here's the next one: speculating
  after RET instructions and leaking privileged information using the
  now pretty much classical covert channels.

  It is called RETBleed and the mitigation effort and controlling
  functionality has been modelled similar to what already existing
  mitigations provide"

* tag 'x86_bugs_retbleed' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits)
  x86/speculation: Disable RRSBA behavior
  x86/kexec: Disable RET on kexec
  x86/bugs: Do not enable IBPB-on-entry when IBPB is not supported
  x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry
  x86/bugs: Add Cannon lake to RETBleed affected CPU list
  x86/retbleed: Add fine grained Kconfig knobs
  x86/cpu/amd: Enumerate BTC_NO
  x86/common: Stamp out the stepping madness
  KVM: VMX: Prevent RSB underflow before vmenter
  x86/speculation: Fill RSB on vmexit for IBRS
  KVM: VMX: Fix IBRS handling after vmexit
  KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
  KVM: VMX: Convert launched argument to flags
  KVM: VMX: Flatten __vmx_vcpu_run()
  objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}
  x86/speculation: Remove x86_spec_ctrl_mask
  x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit
  x86/speculation: Fix SPEC_CTRL write on SMT state change
  x86/speculation: Fix firmware entry SPEC_CTRL handling
  x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n
  ...

x86: Fix .brk attribute in linker script

2022-07-01T09:12:43+00:00

Commit in Fixes added the "NOLOAD" attribute to the .brk section as a
"failsafe" measure.

Unfortunately, this leads to the linker no longer covering the .brk
section in a program header, resulting in the kernel loader not knowing
that the memory for the .brk section must be reserved.

This has led to crashes when loading the kernel as PV dom0 under Xen,
but other scenarios could be hit by the same problem (e.g. in case an
uncompressed kernel is used and the initrd is placed directly behind
it).

So drop the "NOLOAD" attribute. This has been verified to correctly
cover the .brk section by a program header of the resulting ELF file.

Fixes: e32683c6f7d2 ("x86/mm: Fix RESERVE_BRK() for older binutils")
Signed-off-by: Juergen Gross 
Signed-off-by: Borislav Petkov 
Reviewed-by: Josh Poimboeuf 
Link: https://lore.kernel.org/r/20220630071441.28576-4-jgross@suse.com

x86: Add magic AMD return-thunk

2022-06-27T08:33:59+00:00

Note: needs to be in a section distinct from Retpolines such that the
Retpoline RET substitution cannot possibly use immediate jumps.

ORC unwinding for zen_untrain_ret() and __x86_return_thunk() is a
little tricky but works due to the fact that zen_untrain_ret() doesn't
have any stack ops and as such will emit a single ORC entry at the
start (+0x3f).

Meanwhile, unwinding an IP, including the __x86_return_thunk() one
(+0x40) will search for the largest ORC entry smaller or equal to the
IP, these will find the one ORC entry (+0x3f) and all works.

  [ Alexandre: SVM part. ]
  [ bp: Build fix, massages. ]

Suggested-by: Andrew Cooper 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86: Undo return-thunk damage

2022-06-27T08:33:58+00:00

Introduce X86_FEATURE_RETHUNK for those afflicted with needing this.

  [ bp: Do only INT3 padding - simpler. ]

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Borislav Petkov 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Borislav Petkov

x86/mm: Fix RESERVE_BRK() for older binutils

2022-06-13T08:15:04+00:00

With binutils 2.26, RESERVE_BRK() causes a build failure:

/tmp/ccnGOKZ5.s: Assembler messages:
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: missing ')'
/tmp/ccnGOKZ5.s:98: Error: junk at end of line, first unrecognized
character is `U'

The problem is this line:

RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE)

Specifically, the INIT_PGT_BUF_SIZE macro which (via PAGE_SIZE's use
_AC()) has a "1UL", which makes older versions of the assembler unhappy.
Unfortunately the _AC() macro doesn't work for inline asm.

Inline asm was only needed here to convince the toolchain to add the
STT_NOBITS flag. However, if a C variable is placed in a section whose
name is prefixed with ".bss", GCC and Clang automatically set
STT_NOBITS. In fact, ".bss..page_aligned" already relies on this trick.

So fix the build failure (and simplify the macro) by allocating the
variable in C.

Also, add NOLOAD to the ".brk" output section clause in the linker
script. This is a failsafe in case the ".bss" prefix magic trick ever
stops working somehow. If there's a section type mismatch, the GNU
linker will force the ".brk" output section to be STT_NOBITS. The LLVM
linker will fail with a "section type mismatch" error.

Note this also changes the name of the variable from .brk.##name to
__brk_##name. The variable names aren't actually used anywhere, so it's
harmless.

Fixes: a1e2c031ec39 ("x86/mm: Simplify RESERVE_BRK()")
Reported-by: Joe Damato
Reported-by: Byungchul Park
Signed-off-by: Josh Poimboeuf
Signed-off-by: Peter Zijlstra (Intel)
Tested-by: Joe Damato
Link: https://lore.kernel.org/r/22d07a44c80d8e8e1e82b9a806ddc8c6bbb2606e.1654759036.git.jpoimboe@kernel.org

x86: remove the IOMMU table infrastructure

2022-04-18T05:21:10+00:00

The IOMMU table tries to separate the different IOMMUs into different
backends, but actually requires various cross calls.

Rewrite the code to do the generic swiotlb/swiotlb-xen setup directly
in pci-dma.c and then just call into the IOMMU drivers.

Signed-off-by: Christoph Hellwig 
Reviewed-by: Konrad Rzeszutek Wilk 
Tested-by: Boris Ostrovsky