Cache the dont_correlate() result once per symbol at the start of
correlate_symbols(). This reduces klp diff time on an arm64 LTO
vmlinux.o from 2m51s to 35s.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Only create prefix symbols for functions that have
__patchable_function_entries entries, since those are the only C
functions where prefix NOPs are intentional.
This both simplifies the detection and makes it more accurate.
Note that assembly functions using SYM_TYPED_FUNC_START() can also have
prefixed NOPs, but that macro already creates their __cfi_ symbols.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
With CFI+CALL_PADDING, Clang places .Ltmp labels at the start of the NOP
padding (offset 5) between the __cfi_ prefix and the function entry
point. get_func_prefix() only checks the immediately previous symbol,
so the intervening .Ltmp label causes it to miss the __cfi_ prefix
symbol.
This results in klp-diff not cloning the kCFI type hash into the
livepatch module, causing a CFI failure at module load when calling
callback functions through indirect calls:
CFI failure at __klp_enable_patch+0xab/0x140
(target: pre_patch_callback+0x0/0x80 [livepatch_combined];
expected type: 0xde073954)
Instead of walking backward through the section's symbol list, just use
find_func_containing() for the byte before the function. This works now
that __cfi_ symbols are being grown by objtool to fill the padding.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
For all CONFIG_CFI+CONFIG_CALL_PADDING configs, for C functions, the
__cfi_ symbols only cover the 5-byte kCFI type hash. After that there
also N bytes of NOP padding between the hash and the function entry
which aren't associated with any symbol.
The NOPs can be replaced with actual code at runtime. Without a symbol,
unwinders and tooling have no way of knowing where those bytes belong.
Grow the existing __cfi_* symbols to fill that gap.
Note that assembly functions with SYM_TYPED_FUNC_START() aren't affected
by this issue, their __cfi_ symbols also cover the padding.
Also, CONFIG_PREFIX_SYMBOLS has no reason to exist: CONFIG_CALL_PADDING
is what causes the compiler to emit NOP padding before function entry
(via -fpatchable-function-entry), so it's the right condition for
creating prefix symbols.
Remove CONFIG_PREFIX_SYMBOLS, as it's no longer needed. Simplify the
LONGEST_SYM_KUNIT_TEST dependency accordingly. Rework objtool's
arguments a bit to handle the variety of prefix/cfi-related cases.
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
When computing klp checksums, instructions with non-relocated jump/call
destination offsets are problematic because the offset values can change
when surrounding code has moved, causing the function to be incorrectly
marked as changed.
Specifically, that includes jumps from alternatives to the end of the
alternative, which from objtool's perspective are jumps to the end of
the alternative instruction block in the original function.
Note that 'jump_dest' jumps don't include sibling calls (those use
call_dest), nor do they include jumps to/from .cold sub functions (those
are cross-section and need a reloc).
Fix it by hashing the opcode bytes (excluding the immediate operand)
along with a position-independent representation of the destination.
For calls, use the function name, and for jumps, use the destination's
offset within its function.
[Note the "9 bit hole" comment was wrong: it has been 8 bits since
commit 70589843b3 ("objtool: Add option to trace function validation")
added the 'trace' field. Adding the 4-bit 'immediate_len' field now
leaves a 4-bit hole.]
Fixes: 0d83da43b1 ("objtool/klp: Add --checksum option to generate per-function checksums")
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Alternative replacement instructions awkwardly have insn->sym set to the
function they get patched to rather than the symbol (or rather lack
thereof) they belong to in the file.
This makes it difficult to know where a given instruction actually
lives.
Add a new insn_sym() helper which preserves the existing semantic of
insn->sym. Rename insn->sym to insn->_sym, which contains the actual
ELF binary symbol (or NULL, for alternative replacements) an instruction
lives in.
The private insn->_sym value will be needed for a subsequent patch.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Add debugging messages to show how duplicate symbols get correlated, and
split the --debug feature into --debug-correlate and --debug-clone.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Rewrite the symbol correlation code, using a tiered list of
deterministic strategies in a loop. For duplicately named symbols, each
tier applies a filter with the goal of finding a 1:1 deterministic
correlation between the original and patched version of the symbol.
The three matching strategies are:
find_twin(): A funnel of progressively tighter filters. Candidates
with the same demangled name are counted at four levels: name, scope
(local-vs-global), file (strict file association), and checksum
(unchanged functions). The widest level that yields a 1:1 match wins,
narrower levels are only tried when the wider level is ambiguous.
find_twin_suffixed(): Uses already-correlated LLVM symbol pairs to map
.llvm.<hash> suffixes from orig to patched. Because all promoted
symbols from the same TU share the same hash, one correlated pair
seeds the mapping for the entire TU.
find_twin_positional(): Last resort, matches symbols by position among
same-named candidates, similar to livepatch sympos. Used for data
objects like __quirk variables where no deterministic filter can
distinguish the candidates.
Overall this works much better than the existing algorithm, particularly
with LTO kernels.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Start checksumming data objects in preparation for revamping the
correlation algorithm.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
The checksum functionality has been moved to "objtool klp checksum"
which is now used by klp-build. Remove the now-dead --checksum and
--debug-checksum options from the default objtool command.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Move the checksum functionality out of the main objtool command into a
new "objtool klp checksum" subcommand.
This has the benefit of making the code (and the patch generation
process itself) more modular.
For bisectability, both "objtool --checksum" and "objtool klp checksum"
work for now. The former will be removed after klp-build has been
converted to use the new subcommand.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
decode_sections() relies on CFI and cfi_hash initialization done
separately in check(), making it unusable outside of check().
Consolidate the initialization into decode_sections() and rename it to
decode_file(), and make it global along with free_insns() and
insn_reloc() for use by other objtool components -- namely, the checksum
code which will be moving to another file.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
In preparation for porting the checksum code to other arches, make its
functionality independent from the CFG reverse engineering code.
Move it into a standalone calculate_checksums() function which iterates
all functions and instructions directly, rather than being called inline
from do_validate_branch().
Since checksum_update_insn() is no longer called during CFG traversal,
it needs to manually iterate the alternatives.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Improve readability with a new is_alias_sym() helper.
No functional changes intended.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Clang generates anonymous data sections named .data..Lanon.<hash>.
These need section-symbol references in the same way as .data..Lubsan
(GCC) and .data..L__unnamed_ (Clang UBSAN) sections. Without this,
convert_reloc_sym() fails when processing relocations that reference
these sections.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
If an object file has no functions, objtool has nothing to checksum, so
it doesn't create the .discard.sym_checksum symbol.
Then when 'objtool klp diff' reads symbol checksums, it errors out due
to the missing .discard.sym_checksum section.
Instead, just create an empty checksum section to signal to
read_sym_checksums() that the file has been processed.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Instead of installing libsubcmd headers to a build output directory and
including from there, include directly from tools/lib/ where they
already exist. This fixes clangd indexing which otherwise can't find
libsubcmd headers.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Section symbols aren't grouped after their corresponding FILE symbols.
Their sym->file should really be NULL rather than whatever random FILE
happened to be last.
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
In find_reloc_by_dest_range(), hash collisions can cause a high-offset
relocation to appear when probing a low-offset hash bucket.
Only return early when the best match found so far genuinely belongs to
the current bucket (its offset is within the bucket's stride range).
Otherwise, continue scanning later buckets which may contain
lower-offset matches.
This ensures the first reloc in the range gets returned.
Fixes: 74b873e49d ("objtool: Optimize find_rela_by_dest_range()")
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Use the section symbol's index instead of the old symbol's index when
updating the ELF relocation entry in convert_reloc_sym_to_secsym().
Found by Sashiko review.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Clang aggregates UBSAN type descriptors into shared anonymous
.data..L__unnamed_* sections. This data is used by UBSAN trap handlers.
When a changed function has an UBSAN bounds check, klp-diff clones the
entire UBSAN data section associated with the TU. Relocations within
the cloned section that reference named rodata objects in .rodata.cst*
(like 'exponent', 'pirq_ali_set.irqmap') become KLP relocations because
those objects now get correlated.
That results in a .klp.rela.vmlinux..data section which can easily have
thousands of KLP relocs, most of which are completely superfluous, used
by functions which aren't cloned to the patch module.
The .rodata.cst* sections are SHF_MERGE constant pool sections
containing small fixed-size data (lookup tables, bitmasks) that is only
read by value. Pointer identity is never relevant for these objects, so
correlating them is unnecessary.
Exclude .rodata.cst* objects from correlation so they get cloned as
local data instead of generating KLP relocations.
It might be possible to someday treat UBSAN data sections as special
sections, and only extract the few needed entries. But this works for
now.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
klp-diff treats all rodata as uncorrelated, so any reference to it uses
a duplicated copy rather than using a KLP reloc.
For the contents of the data itself, a duplicated copy is fine.
However, pointer comparisons (e.g., f->f_op == &foo_ops) are broken.
Fix it by correlating non-anonymous rodata objects.
Also, use a new find_symbol_containing_inclusive() helper for matching
the end of a symbol so bounds calculations don't get broken, for the
case where an array or other symbol's ending address is used as part of
a bounds calculation.
While these are really two distinct changes, they need to be done in the
same patch so as to avoid introducing bisection regressions.
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Inline section_reference_needed() and is_reloc_allowed() into
convert_reloc_sym() and remove the redundant is_reloc_allowed() check in
clone_reloc().
Move the is_sec_sym() checks into the convert callees so they become
no-ops when the reloc is already in the right format. This allows
convert_reloc_sym() to unconditionally dispatch to the right converter
based on section type.
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Miguel Ojeda
Josh Poimboeuf