x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 208 insertions, 0 deletions

diff --git a/tools/bootconfig/test-bootconfig.sh b/tools/bootconfig/test-bootconfig.sh
new file mode 100755
index 000000000..fc69f815c
--- /dev/null
+++ b/tools/bootconfig/test-bootconfig.sh
@@ -0,0 +1,208 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+echo "Boot config test script"
+
+if [ -d "$1" ]; then
+  TESTDIR=$1
+else
+  TESTDIR=.
+fi
+BOOTCONF=${TESTDIR}/bootconfig
+ALIGN=4
+
+INITRD=`mktemp ${TESTDIR}/initrd-XXXX`
+TEMPCONF=`mktemp ${TESTDIR}/temp-XXXX.bconf`
+OUTFILE=`mktemp ${TESTDIR}/tempout-XXXX`
+NG=0
+
+cleanup() {
+  rm -f $INITRD $TEMPCONF $OUTFILE
+  exit $NG
+}
+
+trap cleanup EXIT TERM
+
+NO=1
+
+xpass() { # pass test command
+  echo "test case $NO ($*)... "
+  if ! ($@ && printf "\t\t[OK]\n"); then
+     printf "\t\t[NG]\n"; NG=$((NG + 1))
+  fi
+  NO=$((NO + 1))
+}
+
+xfail() { # fail test command
+  echo "test case $NO ($*)... "
+  if ! (! $@ && printf "\t\t[OK]\n"); then
+     printf "\t\t[NG]\n"; NG=$((NG + 1))
+  fi
+  NO=$((NO + 1))
+}
+
+echo "Basic command test"
+xpass $BOOTCONF $INITRD
+
+echo "Delete command should success without bootconfig"
+xpass $BOOTCONF -d $INITRD
+
+dd if=/dev/zero of=$INITRD bs=4096 count=1
+printf "key = value;" > $TEMPCONF
+bconf_size=$(wc -c < $TEMPCONF)
+initrd_size=$(wc -c < $INITRD)
+
+echo "Apply command test"
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+new_size=$(wc -c < $INITRD)
+
+echo "Show command test"
+xpass $BOOTCONF $INITRD
+
+echo "File size check"
+total_size=$(expr $bconf_size + $initrd_size + 9 + 12 + $ALIGN - 1 )
+total_size=$(expr $total_size / $ALIGN)
+total_size=$(expr $total_size \* $ALIGN)
+xpass test $new_size -eq $total_size
+
+echo "Apply command repeat test"
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "File size check"
+xpass test $new_size -eq $(wc -c < $INITRD)
+
+echo "Delete command check"
+xpass $BOOTCONF -d $INITRD
+
+echo "File size check"
+new_size=$(wc -c < $INITRD)
+xpass test $new_size -eq $initrd_size
+
+echo "No error messge while applying"
+dd if=/dev/zero of=$INITRD bs=4096 count=1
+printf " \0\0\0 \0\0\0" >> $INITRD
+$BOOTCONF -a $TEMPCONF $INITRD > $OUTFILE 2>&1
+xfail grep -i "failed" $OUTFILE
+xfail grep -i "error" $OUTFILE
+
+echo "Max node number check"
+
+awk '
+BEGIN {
+  for (i = 0; i < 26; i += 1)
+      printf("%c\n", 65 + i % 26)
+  for (i = 26; i < 8192; i += 1)
+      printf("%c%c%c\n", 65 + i % 26, 65 + (i / 26) % 26, 65 + (i / 26 / 26))
+}
+' > $TEMPCONF
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+printf "badnode\n" >> $TEMPCONF
+xfail $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "Max filesize check"
+
+# Max size is 32767 (including terminal byte)
+printf "data = \"" > $TEMPCONF
+dd if=/dev/urandom bs=768 count=32 | base64 -w0 >> $TEMPCONF
+printf "\"\n" >> $TEMPCONF
+xfail $BOOTCONF -a $TEMPCONF $INITRD
+
+dd if=$TEMPCONF of=$OUTFILE bs=1 count=32764
+cp $OUTFILE $TEMPCONF
+printf "\"\n" >> $TEMPCONF	# add 2 bytes + terminal ('\"\n\0')
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+
+echo "Adding same-key values"
+cat > $TEMPCONF << EOF
+key = bar, baz
+key += qux
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xpass grep -q "bar" $OUTFILE
+xpass grep -q "baz" $OUTFILE
+xpass grep -q "qux" $OUTFILE
+
+echo "Override same-key values"
+cat > $TEMPCONF << EOF
+key = bar, baz
+key := qux
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xfail grep -q "bar" $OUTFILE
+xfail grep -q "baz" $OUTFILE
+xpass grep -q "qux" $OUTFILE
+
+echo "Double/single quotes test"
+printf "key = '\"string\"';" > $TEMPCONF
+$BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $TEMPCONF
+cat $TEMPCONF
+xpass grep \'\"string\"\' $TEMPCONF
+
+echo "Repeat same-key tree"
+cat > $TEMPCONF << EOF
+foo
+bar
+foo { buz }
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xpass grep -q "bar" $OUTFILE
+
+
+echo "Remove/keep tailing spaces"
+cat > $TEMPCONF << EOF
+foo = val     # comment
+bar = "val2 " # comment
+EOF
+echo > $INITRD
+
+xpass $BOOTCONF -a $TEMPCONF $INITRD
+$BOOTCONF $INITRD > $OUTFILE
+xfail grep -q 'val[[:space:]]' $OUTFILE
+xpass grep -q 'val2[[:space:]]' $OUTFILE
+
+echo "Showing correct line:column of no closing brace"
+cat > $TEMPCONF << EOF
+foo {
+bar {
+}
+EOF
+$BOOTCONF -a $TEMPCONF $INITRD 2> $OUTFILE
+xpass grep -q "1:1" $OUTFILE
+
+echo "=== expected failure cases ==="
+for i in samples/bad-* ; do
+  xfail $BOOTCONF -a $i $INITRD
+done
+
+echo "=== expected success cases ==="
+for i in samples/good-* ; do
+  xpass $BOOTCONF -a $i $INITRD
+  x="samples/exp-"`basename $i`
+  $BOOTCONF $i > $TEMPCONF
+  xpass diff $x $TEMPCONF
+done
+
+
+echo
+echo "=== Summary ==="
+echo "# of Passed: $(expr $NO - $NG - 1)"
+echo "# of Failed: $NG"
+
+echo
+if [ $NG -eq 0 ]; then
+	echo "All tests passed"
+else
+	echo "$NG tests failed"
+	exit 1
+fi