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  1. 02 4月, 2021 5 次提交
  3. 15 3月, 2021 3 次提交
  5. 12 3月, 2021 1 次提交
  7. 25 2月, 2021 1 次提交
  9. 24 2月, 2021 4 次提交
  11. 23 2月, 2021 1 次提交
  13. 17 2月, 2021 2 次提交
  15. 11 2月, 2021 3 次提交
  17. 27 1月, 2021 7 次提交
  19. 22 1月, 2021 2 次提交
  21. 14 1月, 2021 10 次提交
    • J
      objtool: Support stack layout changes in alternatives · c9c324dc
      由 Josh Poimboeuf 提交于 
      The ORC unwinder showed a warning [1] which revealed the stack layout
didn't match what was expected.  The problem was that paravirt patching
had replaced "CALL *pv_ops.irq.save_fl" with "PUSHF;POP".  That changed
the stack layout between the PUSHF and the POP, so unwinding from an
interrupt which occurred between those two instructions would fail.

Part of the agreed upon solution was to rework the custom paravirt
patching code to use alternatives instead, since objtool already knows
how to read alternatives (and converging runtime patching infrastructure
is always a good thing anyway).  But the main problem still remains,
which is that runtime patching can change the stack layout.

Making stack layout changes in alternatives was disallowed with commit
7117f16b ("objtool: Fix ORC vs alternatives"), but now that paravirt
is going to be doing it, it needs to be supported.

One way to do so would be to modify the ORC table when the code gets
patched.  But ORC is simple -- a good thing! -- and it's best to leave
it alone.

Instead, support stack layout changes by "flattening" all possible stack
states (CFI) from parallel alternative code streams into a single set of
linear states.  The only necessary limitation is that CFI conflicts are
disallowed at all possible instruction boundaries.

For example, this scenario is allowed:

          Alt1                    Alt2                    Alt3

   0x00   CALL *pv_ops.save_fl    CALL xen_save_fl        PUSHF
   0x01                                                   POP %RAX
   0x02                                                   NOP
   ...
   0x05                           NOP
   ...
   0x07   <insn>

The unwind information for offset-0x00 is identical for all 3
alternatives.  Similarly offset-0x05 and higher also are identical (and
the same as 0x00).  However offset-0x01 has deviating CFI, but that is
only relevant for Alt3, neither of the other alternative instruction
streams will ever hit that offset.

This scenario is NOT allowed:

          Alt1                    Alt2

   0x00   CALL *pv_ops.save_fl    PUSHF
   0x01                           NOP6
   ...
   0x07   NOP                     POP %RAX

The problem here is that offset-0x7, which is an instruction boundary in
both possible instruction patch streams, has two conflicting stack
layouts.

[ The above examples were stolen from Peter Zijlstra. ]

The new flattened CFI array is used both for the detection of conflicts
(like the second example above) and the generation of linear ORC
entries.

BTW, another benefit of these changes is that, thanks to some related
cleanups (new fake nops and alt_group struct) objtool can finally be rid
of fake jumps, which were a constant source of headaches.

[1] https://lkml.kernel.org/r/20201111170536.arx2zbn4ngvjoov7@treble

Cc: Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      c9c324dc
    • J
      objtool: Add 'alt_group' struct · b23cc71c
      由 Josh Poimboeuf 提交于 
      Create a new struct associated with each group of alternatives
instructions.  This will help with the removal of fake jumps, and more
importantly with adding support for stack layout changes in
alternatives.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      b23cc71c
    • J
      objtool: Refactor ORC section generation · ab4e0744
      由 Josh Poimboeuf 提交于 
      Decouple ORC entries from instructions.  This simplifies the
control/data flow, and is going to make it easier to support alternative
instructions which change the stack layout.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      ab4e0744
    • V
      objtool: Rework header include paths · 7786032e
      由 Vasily Gorbik 提交于 
      Currently objtool headers are being included either by their base name
or included via ../ from a parent directory. In case of a base name usage:

 #include "warn.h"
 #include "arch_elf.h"

it does not make it apparent from which directory the file comes from.
To make it slightly better, and actually to avoid name clashes some arch
specific files have "arch_" suffix. And files from an arch folder have
to revert to including via ../ e.g:
 #include "../../elf.h"

With additional architectures support and the code base growth there is
a need for clearer headers naming scheme for multiple reasons:
1. to make it instantly obvious where these files come from (objtool
   itself / objtool arch|generic folders / some other external files),
2. to avoid name clashes of objtool arch specific headers, potential
   obtool arch generic headers and the system header files (there is
   /usr/include/elf.h already),
3. to avoid ../ includes and improve code readability.
4. to give a warm fuzzy feeling to developers who are mostly kernel
   developers and are accustomed to linux kernel headers arranging
   scheme.

Doesn't this make it instantly obvious where are these files come from?

 #include <objtool/warn.h>
 #include <arch/elf.h>

And doesn't it look nicer to avoid ugly ../ includes? Which also
guarantees this is elf.h from the objtool and not /usr/include/elf.h.

 #include <objtool/elf.h>

This patch defines and implements new objtool headers arranging
scheme. Which is:
- all generic headers go to include/objtool (similar to include/linux)
- all arch headers go to arch/$(SRCARCH)/include/arch (to get arch
  prefix). This is similar to linux arch specific "asm/*" headers but we
  are not abusing "asm" name and calling it what it is. This also helps
  to prevent name clashes (arch is not used in system headers or kernel
  exports).

To bring objtool to this state the following things are done:
1. current top level tools/objtool/ headers are moved into
   include/objtool/ subdirectory,
2. arch specific headers, currently only arch/x86/include/ are moved into
   arch/x86/include/arch/ and were stripped of "arch_" suffix,
3. new -I$(srctree)/tools/objtool/include include path to make
   includes like <objtool/warn.h> possible,
4. rewriting file includes,
5. make git not to ignore include/objtool/ subdirectory.
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      7786032e
    • V
      objtool: Fix x86 orc generation on big endian cross-compiles · 8bfe2732
      由 Vasily Gorbik 提交于 
      Correct objtool orc generation endianness problems to enable fully
functional x86 cross-compiles on big endian hardware.

Introduce bswap_if_needed() macro, which does a byte swap if target
endianness doesn't match the host, i.e. cross-compilation for little
endian on big endian and vice versa.  The macro is used for conversion
of multi-byte values which are read from / about to be written to a
target native endianness ELF file.
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      8bfe2732
    • M
      objtool: Fix reloc generation on big endian cross-compiles · a1a664ec
      由 Martin Schwidefsky 提交于 
      Relocations generated in elf_rebuild_rel[a]_reloc_section() are broken
if objtool is built and run on a big endian system.

The following errors pop up during x86 cross-compilation:

  x86_64-9.1.0-ld: fs/efivarfs/inode.o: bad reloc symbol index (0x2000000 >= 0x22) for offset 0 in section `.orc_unwind_ip'
  x86_64-9.1.0-ld: final link failed: bad value

Convert those functions to use gelf_update_rel[a](), similar to what
elf_write_reloc() does.
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>
Co-developed-by: NVasily Gorbik <gor@linux.ibm.com>
Signed-off-by: NVasily Gorbik <gor@linux.ibm.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      a1a664ec
    • J
      objtool: Make SP memory operation match PUSH/POP semantics · 201ef5a9
      由 Julien Thierry 提交于 
      Architectures without PUSH/POP instructions will always access the stack
though memory operations (SRC/DEST_INDIRECT). Make those operations have
the same effect on the CFA as PUSH/POP, with no stack pointer
modification.
Signed-off-by: NJulien Thierry <jthierry@redhat.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      201ef5a9
    • J
      objtool: Support addition to set CFA base · 468af56a
      由 Julien Thierry 提交于 
      On arm64, the compiler can set the frame pointer either
with a move operation or with and add operation like:

    add (SP + constant), BP

For a simple move operation, the CFA base is changed from SP to BP.
Handle also changing the CFA base when the frame pointer is set with
an addition instruction.
Signed-off-by: NJulien Thierry <jthierry@redhat.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      468af56a
    • J
      objtool: Fully validate the stack frame · fb084fde
      由 Julien Thierry 提交于 
      A valid stack frame should contain both the return address and the
previous frame pointer value.

On x86, the return value is placed on the stack by the calling
instructions. On other architectures, the callee needs to explicitly
save the return address on the stack.

Add the necessary checks to verify a function properly sets up all the
elements of the stack frame.
Signed-off-by: NJulien Thierry <jthierry@redhat.com>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      fb084fde
    • J
      objtool: Don't add empty symbols to the rbtree · a2e38dff
      由 Josh Poimboeuf 提交于 
      Building with the Clang assembler shows the following warning:

  arch/x86/kernel/ftrace_64.o: warning: objtool: missing symbol for insn at offset 0x16

The Clang assembler strips section symbols.  That ends up giving
objtool's find_func_containing() much more test coverage than normal.
Turns out, find_func_containing() doesn't work so well for overlapping
symbols:

     2: 000000000000000e     0 NOTYPE  LOCAL  DEFAULT    2 fgraph_trace
     3: 000000000000000f     0 NOTYPE  LOCAL  DEFAULT    2 trace
     4: 0000000000000000   165 FUNC    GLOBAL DEFAULT    2 __fentry__
     5: 000000000000000e     0 NOTYPE  GLOBAL DEFAULT    2 ftrace_stub

The zero-length NOTYPE symbols are inside __fentry__(), confusing the
rbtree search for any __fentry__() offset coming after a NOTYPE.

Try to avoid this problem by not adding zero-length symbols to the
rbtree.  They're rare and aren't needed in the rbtree anyway.

One caveat, this actually might not end up being the right fix.
Non-empty overlapping symbols, if they exist, could have the same
problem.  But that would need bigger changes, let's see if we can get
away with the easy fix for now.
Reported-by: NArnd Bergmann <arnd@kernel.org>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
      a2e38dff
  23. 16 12月, 2020 1 次提交