[PATCH v2 2/2] perf symbols: skip livepatch symbols in kcore_copy kallsyms processing

Livepatch symbols (.klp.sym.*) carry a [module] tag but resolve to core
kernel text addresses.  When kcore_copy__process_kallsyms() encounters
these symbols, they are treated as module symbols, pulling the
first_module_symbol down to a kernel text address.

This corrupts the module memory range used to build the kcore PT_LOAD
segments.  For example, with a kpatch module containing a
".klp.sym.vmlinux.arch_release_task_struct,0" livepatch symbol loaded:

  kernel symbols
    ...
    ffffffffb4a41120  arch_release_task_struct
    ...                 ^
    ...                 | aliased by .klp.sym
    ...                 | drags first_module_symbol here
                        |
    (43M gap)           | bloated kcore segment
                        |
  module symbols        |
    ffffffffc047b000  <-- correct first_module_symbol
    ...
    ...

This causes the module PT_LOAD segment to start at the .klp.sym address
and not the real first module address, bloating the kcore copy:

  Baseline (no livepatch):   VirtAddr ffffffffc047b000, 8.5M
  Bloated  (with livepatch): VirtAddr ffffffffb4a41000, 54M
  Post-fix (with livepatch): VirtAddr ffffffffc047b000, 8.9M

Filter livepatch symbols early in kcore_copy__process_kallsyms() before
they can affect module boundary tracking.

Reported-by: Sashiko <[email protected]>
Link: https://sashiko.dev/#/patchset/[email protected]?part=1
Signed-off-by: Joe Lawrence <[email protected]>
---
 tools/perf/util/symbol-elf.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 39562bdec8b9..f6f6b54da131 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -2216,6 +2216,10 @@ static int kcore_copy__process_kallsyms(void *arg, const char *name, char type,
 	if (!kallsyms__is_function(type))
 		return 0;
 
+	/* Ignore livepatch symbols */
+	if (is_livepatch_symbol(name))
+		return 0;
+
 	if (strchr(name, '[')) {
 		if (!kci->first_module_symbol || start < kci->first_module_symbol)
 			kci->first_module_symbol = start;
-- 
2.54.0