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, 216 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/keyhelp.c b/drivers/accessibility/speakup/keyhelp.c
new file mode 100644
index 000000000..0940f430a
--- /dev/null
+++ b/drivers/accessibility/speakup/keyhelp.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* speakup_keyhelp.c
+ * help module for speakup
+ *
+ *written by David Borowski.
+ *
+ *  Copyright (C) 2003  David Borowski.
+ */
+
+#include <linux/keyboard.h>
+#include <linux/ctype.h>
+#include "spk_priv.h"
+#include "speakup.h"
+
+#define MAXFUNCS 130
+#define MAXKEYS 256
+static const int num_key_names = MSG_KEYNAMES_END - MSG_KEYNAMES_START + 1;
+static u16 key_offsets[MAXFUNCS], key_data[MAXKEYS];
+static u16 masks[] = { 32, 16, 8, 4, 2, 1 };
+
+static short letter_offsets[26] = {
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1, -1, -1, -1, -1, -1, -1,
+	-1, -1 };
+
+static u_char funcvals[] = {
+	ATTRIB_BLEEP_DEC, ATTRIB_BLEEP_INC, BLEEPS_DEC, BLEEPS_INC,
+	SAY_FIRST_CHAR, SAY_LAST_CHAR, SAY_CHAR, SAY_CHAR_NUM,
+	SAY_NEXT_CHAR, SAY_PHONETIC_CHAR, SAY_PREV_CHAR, SPEAKUP_PARKED,
+	SPEAKUP_CUT, EDIT_DELIM, EDIT_EXNUM, EDIT_MOST,
+	EDIT_REPEAT, EDIT_SOME, SPEAKUP_GOTO, BOTTOM_EDGE,
+	LEFT_EDGE, RIGHT_EDGE, TOP_EDGE, SPEAKUP_HELP,
+	SAY_LINE, SAY_NEXT_LINE, SAY_PREV_LINE, SAY_LINE_INDENT,
+	SPEAKUP_PASTE, PITCH_DEC, PITCH_INC, PUNCT_DEC,
+	PUNCT_INC, PUNC_LEVEL_DEC, PUNC_LEVEL_INC, SPEAKUP_QUIET,
+	RATE_DEC, RATE_INC, READING_PUNC_DEC, READING_PUNC_INC,
+	SAY_ATTRIBUTES, SAY_FROM_LEFT, SAY_FROM_TOP, SAY_POSITION,
+	SAY_SCREEN, SAY_TO_BOTTOM, SAY_TO_RIGHT, SPK_KEY,
+	SPK_LOCK, SPEAKUP_OFF, SPEECH_KILL, SPELL_DELAY_DEC,
+	SPELL_DELAY_INC, SPELL_WORD, SPELL_PHONETIC, TONE_DEC,
+	TONE_INC, VOICE_DEC, VOICE_INC, VOL_DEC,
+	VOL_INC, CLEAR_WIN, SAY_WIN, SET_WIN,
+	ENABLE_WIN, SAY_WORD, SAY_NEXT_WORD, SAY_PREV_WORD, 0
+};
+
+static u_char *state_tbl;
+static int cur_item, nstates;
+
+static void build_key_data(void)
+{
+	u_char *kp, counters[MAXFUNCS], ch, ch1;
+	u16 *p_key, key;
+	int i, offset = 1;
+
+	nstates = (int)(state_tbl[-1]);
+	memset(counters, 0, sizeof(counters));
+	memset(key_offsets, 0, sizeof(key_offsets));
+	kp = state_tbl + nstates + 1;
+	while (*kp++) {
+		/* count occurrences of each function */
+		for (i = 0; i < nstates; i++, kp++) {
+			if (!*kp)
+				continue;
+			if ((state_tbl[i] & 16) != 0 && *kp == SPK_KEY)
+				continue;
+			counters[*kp]++;
+		}
+	}
+	for (i = 0; i < MAXFUNCS; i++) {
+		if (counters[i] == 0)
+			continue;
+		key_offsets[i] = offset;
+		offset += (counters[i] + 1);
+		if (offset >= MAXKEYS)
+			break;
+	}
+/* leave counters set so high keycodes come first.
+ * this is done so num pad and other extended keys maps are spoken before
+ * the alpha with speakup type mapping.
+ */
+	kp = state_tbl + nstates + 1;
+	while ((ch = *kp++)) {
+		for (i = 0; i < nstates; i++) {
+			ch1 = *kp++;
+			if (!ch1)
+				continue;
+			if ((state_tbl[i] & 16) != 0 && ch1 == SPK_KEY)
+				continue;
+			key = (state_tbl[i] << 8) + ch;
+			counters[ch1]--;
+			offset = key_offsets[ch1];
+			if (!offset)
+				continue;
+			p_key = key_data + offset + counters[ch1];
+			*p_key = key;
+		}
+	}
+}
+
+static void say_key(int key)
+{
+	int i, state = key >> 8;
+
+	key &= 0xff;
+	for (i = 0; i < 6; i++) {
+		if (state & masks[i])
+			synth_printf(" %s", spk_msg_get(MSG_STATES_START + i));
+	}
+	if ((key > 0) && (key <= num_key_names))
+		synth_printf(" %s\n",
+			     spk_msg_get(MSG_KEYNAMES_START + (key - 1)));
+}
+
+static void help_init(void)
+{
+	char start = SPACE;
+	int i;
+	int num_funcs = MSG_FUNCNAMES_END - MSG_FUNCNAMES_START + 1;
+
+	state_tbl = spk_our_keys[0] + SHIFT_TBL_SIZE + 2;
+	for (i = 0; i < num_funcs; i++) {
+		char *cur_funcname = spk_msg_get(MSG_FUNCNAMES_START + i);
+		char first_letter;
+
+		first_letter = tolower(*cur_funcname);
+
+		/* Accept only 'a'..'z' to index letter_offsets[] safely */
+		if (first_letter < 'a' || first_letter > 'z')
+			continue;
+
+		if (start == first_letter)
+			continue;
+		start = first_letter;
+		letter_offsets[(start & 31) - 1] = i;
+	}
+}
+
+int spk_handle_help(struct vc_data *vc, u_char type, u_char ch, u16 key)
+{
+	int i, n;
+	char *name;
+	u_char func, *kp;
+	u16 *p_keys, val;
+
+	if (letter_offsets[0] == -1)
+		help_init();
+	if (type == KT_LATIN) {
+		if (ch == SPACE) {
+			spk_special_handler = NULL;
+			synth_printf("%s\n", spk_msg_get(MSG_LEAVING_HELP));
+			return 1;
+		}
+		ch = tolower(ch);
+		if (ch < 'a' || ch > 'z')
+			return -1;
+		if (letter_offsets[ch - 'a'] == -1) {
+			synth_printf(spk_msg_get(MSG_NO_COMMAND), ch);
+			synth_printf("\n");
+			return 1;
+		}
+		cur_item = letter_offsets[ch - 'a'];
+	} else if (type == KT_CUR) {
+		if (ch == 0 &&
+		    (MSG_FUNCNAMES_START + cur_item + 1) <= MSG_FUNCNAMES_END)
+			cur_item++;
+		else if (ch == 3 && cur_item > 0)
+			cur_item--;
+		else
+			return -1;
+	} else if (type == KT_SPKUP && ch == SPEAKUP_HELP &&
+		   !spk_special_handler) {
+		spk_special_handler = spk_handle_help;
+		synth_printf("%s\n", spk_msg_get(MSG_HELP_INFO));
+		build_key_data(); /* rebuild each time in case new mapping */
+		return 1;
+	} else {
+		name = NULL;
+		if ((type != KT_SPKUP) && (key > 0) && (key <= num_key_names)) {
+			synth_printf("%s\n",
+				     spk_msg_get(MSG_KEYNAMES_START + key - 1));
+			return 1;
+		}
+		for (i = 0; funcvals[i] != 0 && !name; i++) {
+			if (ch == funcvals[i])
+				name = spk_msg_get(MSG_FUNCNAMES_START + i);
+		}
+		if (!name)
+			return -1;
+		kp = spk_our_keys[key] + 1;
+		for (i = 0; i < nstates; i++) {
+			if (ch == kp[i])
+				break;
+		}
+		key += (state_tbl[i] << 8);
+		say_key(key);
+		synth_printf(spk_msg_get(MSG_KEYDESC), name);
+		synth_printf("\n");
+		return 1;
+	}
+	name = spk_msg_get(MSG_FUNCNAMES_START + cur_item);
+	func = funcvals[cur_item];
+	synth_printf("%s", name);
+	if (key_offsets[func] == 0) {
+		synth_printf(" %s\n", spk_msg_get(MSG_IS_UNASSIGNED));
+		return 1;
+	}
+	p_keys = key_data + key_offsets[func];
+	for (n = 0; p_keys[n]; n++) {
+		val = p_keys[n];
+		if (n > 0)
+			synth_printf("%s ", spk_msg_get(MSG_DISJUNCTION));
+		say_key(val);
+	}
+	return 1;
+}