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, 329 insertions, 0 deletions

diff --git a/arch/m68k/atari/debug.c b/arch/m68k/atari/debug.c
new file mode 100644
index 000000000..03cb5e08d
--- /dev/null
+++ b/arch/m68k/atari/debug.c
@@ -0,0 +1,329 @@
+/*
+ * linux/arch/m68k/atari/debug.c
+ *
+ * Atari debugging and serial console stuff
+ *
+ * Assembled of parts of former atari/config.c 97-12-18 by Roman Hodek
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/types.h>
+#include <linux/tty.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+
+#include <asm/atarihw.h>
+#include <asm/atariints.h>
+
+/* Can be set somewhere, if a SCC master reset has already be done and should
+ * not be repeated; used by kgdb */
+int atari_SCC_reset_done;
+EXPORT_SYMBOL(atari_SCC_reset_done);
+
+static struct console atari_console_driver = {
+	.name	= "debug",
+	.flags	= CON_PRINTBUFFER,
+	.index	= -1,
+};
+
+
+static inline void ata_mfp_out(char c)
+{
+	while (!(st_mfp.trn_stat & 0x80))	/* wait for tx buf empty */
+		barrier();
+	st_mfp.usart_dta = c;
+}
+
+static void atari_mfp_console_write(struct console *co, const char *str,
+				    unsigned int count)
+{
+	while (count--) {
+		if (*str == '\n')
+			ata_mfp_out('\r');
+		ata_mfp_out(*str++);
+	}
+}
+
+static inline void ata_scc_out(char c)
+{
+	do {
+		MFPDELAY();
+	} while (!(atari_scc.cha_b_ctrl & 0x04)); /* wait for tx buf empty */
+	MFPDELAY();
+	atari_scc.cha_b_data = c;
+}
+
+static void atari_scc_console_write(struct console *co, const char *str,
+				    unsigned int count)
+{
+	while (count--) {
+		if (*str == '\n')
+			ata_scc_out('\r');
+		ata_scc_out(*str++);
+	}
+}
+
+static inline void ata_midi_out(char c)
+{
+	while (!(acia.mid_ctrl & ACIA_TDRE))	/* wait for tx buf empty */
+		barrier();
+	acia.mid_data = c;
+}
+
+static void atari_midi_console_write(struct console *co, const char *str,
+				     unsigned int count)
+{
+	while (count--) {
+		if (*str == '\n')
+			ata_midi_out('\r');
+		ata_midi_out(*str++);
+	}
+}
+
+static int ata_par_out(char c)
+{
+	unsigned char tmp;
+	/* This a some-seconds timeout in case no printer is connected */
+	unsigned long i = loops_per_jiffy > 1 ? loops_per_jiffy : 10000000/HZ;
+
+	while ((st_mfp.par_dt_reg & 1) && --i) /* wait for BUSY == L */
+		;
+	if (!i)
+		return 0;
+
+	sound_ym.rd_data_reg_sel = 15;	/* select port B */
+	sound_ym.wd_data = c;		/* put char onto port */
+	sound_ym.rd_data_reg_sel = 14;	/* select port A */
+	tmp = sound_ym.rd_data_reg_sel;
+	sound_ym.wd_data = tmp & ~0x20;	/* set strobe L */
+	MFPDELAY();			/* wait a bit */
+	sound_ym.wd_data = tmp | 0x20;	/* set strobe H */
+	return 1;
+}
+
+static void atari_par_console_write(struct console *co, const char *str,
+				    unsigned int count)
+{
+	static int printer_present = 1;
+
+	if (!printer_present)
+		return;
+
+	while (count--) {
+		if (*str == '\n') {
+			if (!ata_par_out('\r')) {
+				printer_present = 0;
+				return;
+			}
+		}
+		if (!ata_par_out(*str++)) {
+			printer_present = 0;
+			return;
+		}
+	}
+}
+
+#if 0
+int atari_mfp_console_wait_key(struct console *co)
+{
+	while (!(st_mfp.rcv_stat & 0x80))	/* wait for rx buf filled */
+		barrier();
+	return st_mfp.usart_dta;
+}
+
+int atari_scc_console_wait_key(struct console *co)
+{
+	do {
+		MFPDELAY();
+	} while (!(atari_scc.cha_b_ctrl & 0x01)); /* wait for rx buf filled */
+	MFPDELAY();
+	return atari_scc.cha_b_data;
+}
+
+int atari_midi_console_wait_key(struct console *co)
+{
+	while (!(acia.mid_ctrl & ACIA_RDRF)) /* wait for rx buf filled */
+		barrier();
+	return acia.mid_data;
+}
+#endif
+
+/*
+ * The following two functions do a quick'n'dirty initialization of the MFP or
+ * SCC serial ports. They're used by the debugging interface, kgdb, and the
+ * serial console code.
+ */
+static void __init atari_init_mfp_port(int cflag)
+{
+	/*
+	 * timer values for 1200...115200 bps; > 38400 select 110, 134, or 150
+	 * bps, resp., and work only correct if there's a RSVE or RSSPEED
+	 */
+	static int baud_table[9] = { 16, 11, 8, 4, 2, 1, 175, 143, 128 };
+	int baud = cflag & CBAUD;
+	int parity = (cflag & PARENB) ? ((cflag & PARODD) ? 0x04 : 0x06) : 0;
+	int csize = ((cflag & CSIZE) == CS7) ? 0x20 : 0x00;
+
+	if (cflag & CBAUDEX)
+		baud += B38400;
+	if (baud < B1200 || baud > B38400+2)
+		baud = B9600;		/* use default 9600bps for non-implemented rates */
+	baud -= B1200;			/* baud_table[] starts at 1200bps */
+
+	st_mfp.trn_stat &= ~0x01;	/* disable TX */
+	st_mfp.usart_ctr = parity | csize | 0x88; /* 1:16 clk mode, 1 stop bit */
+	st_mfp.tim_ct_cd &= 0x70;	/* stop timer D */
+	st_mfp.tim_dt_d = baud_table[baud];
+	st_mfp.tim_ct_cd |= 0x01;	/* start timer D, 1:4 */
+	st_mfp.trn_stat |= 0x01;	/* enable TX */
+}
+
+#define SCC_WRITE(reg, val)				\
+	do {						\
+		atari_scc.cha_b_ctrl = (reg);		\
+		MFPDELAY();				\
+		atari_scc.cha_b_ctrl = (val);		\
+		MFPDELAY();				\
+	} while (0)
+
+/* loops_per_jiffy isn't initialized yet, so we can't use udelay(). This does a
+ * delay of ~ 60us. */
+#define LONG_DELAY()					\
+	do {						\
+		int i;					\
+		for (i = 100; i > 0; --i)		\
+			MFPDELAY();			\
+	} while (0)
+
+static void __init atari_init_scc_port(int cflag)
+{
+	static int clksrc_table[9] =
+		/* reg 11: 0x50 = BRG, 0x00 = RTxC, 0x28 = TRxC */
+		{ 0x50, 0x50, 0x50, 0x50, 0x50, 0x50, 0x50, 0x00, 0x00 };
+	static int brgsrc_table[9] =
+		/* reg 14: 0 = RTxC, 2 = PCLK */
+		{ 2, 2, 2, 2, 2, 2, 0, 2, 2 };
+	static int clkmode_table[9] =
+		/* reg 4: 0x40 = x16, 0x80 = x32, 0xc0 = x64 */
+		{ 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0x40, 0xc0, 0x80 };
+	static int div_table[9] =
+		/* reg12 (BRG low) */
+		{ 208, 138, 103, 50, 24, 11, 1, 0, 0 };
+
+	int baud = cflag & CBAUD;
+	int clksrc, clkmode, div, reg3, reg5;
+
+	if (cflag & CBAUDEX)
+		baud += B38400;
+	if (baud < B1200 || baud > B38400+2)
+		baud = B9600;		/* use default 9600bps for non-implemented rates */
+	baud -= B1200;			/* tables starts at 1200bps */
+
+	clksrc  = clksrc_table[baud];
+	clkmode = clkmode_table[baud];
+	div     = div_table[baud];
+	if (ATARIHW_PRESENT(TT_MFP) && baud >= 6) {
+		/* special treatment for TT, where rates >= 38400 are done via TRxC */
+		clksrc = 0x28;		/* TRxC */
+		clkmode = baud == 6 ? 0xc0 :
+			  baud == 7 ? 0x80 : /* really 76800bps */
+				      0x40;  /* really 153600bps */
+		div = 0;
+	}
+
+	reg3 = (cflag & CSIZE) == CS8 ? 0xc0 : 0x40;
+	reg5 = (cflag & CSIZE) == CS8 ? 0x60 : 0x20 | 0x82 /* assert DTR/RTS */;
+
+	(void)atari_scc.cha_b_ctrl;	/* reset reg pointer */
+	SCC_WRITE(9, 0xc0);		/* reset */
+	LONG_DELAY();			/* extra delay after WR9 access */
+	SCC_WRITE(4, (cflag & PARENB) ? ((cflag & PARODD) ? 0x01 : 0x03)
+				      : 0 | 0x04 /* 1 stopbit */ | clkmode);
+	SCC_WRITE(3, reg3);
+	SCC_WRITE(5, reg5);
+	SCC_WRITE(9, 0);		/* no interrupts */
+	LONG_DELAY();			/* extra delay after WR9 access */
+	SCC_WRITE(10, 0);		/* NRZ mode */
+	SCC_WRITE(11, clksrc);		/* main clock source */
+	SCC_WRITE(12, div);		/* BRG value */
+	SCC_WRITE(13, 0);		/* BRG high byte */
+	SCC_WRITE(14, brgsrc_table[baud]);
+	SCC_WRITE(14, brgsrc_table[baud] | (div ? 1 : 0));
+	SCC_WRITE(3, reg3 | 1);
+	SCC_WRITE(5, reg5 | 8);
+
+	atari_SCC_reset_done = 1;
+}
+
+static void __init atari_init_midi_port(int cflag)
+{
+	int baud = cflag & CBAUD;
+	int csize = ((cflag & CSIZE) == CS8) ? 0x10 : 0x00;
+	/* warning 7N1 isn't possible! (instead 7O2 is used...) */
+	int parity = (cflag & PARENB) ? ((cflag & PARODD) ? 0x0c : 0x08) : 0x04;
+	int div;
+
+	/* 4800 selects 7812.5, 115200 selects 500000, all other (incl. 9600 as
+	 * default) the standard MIDI speed 31250. */
+	if (cflag & CBAUDEX)
+		baud += B38400;
+	if (baud == B4800)
+		div = ACIA_DIV64;	/* really 7812.5 bps */
+	else if (baud == B38400+2 /* 115200 */)
+		div = ACIA_DIV1;	/* really 500 kbps (does that work??) */
+	else
+		div = ACIA_DIV16;	/* 31250 bps, standard for MIDI */
+
+	/* RTS low, ints disabled */
+	acia.mid_ctrl = div | csize | parity |
+		    ((atari_switches & ATARI_SWITCH_MIDI) ?
+		     ACIA_RHTID : ACIA_RLTID);
+}
+
+static int __init atari_debug_setup(char *arg)
+{
+	bool registered;
+
+	if (!MACH_IS_ATARI)
+		return 0;
+
+	if (!strcmp(arg, "ser"))
+		/* defaults to ser2 for a Falcon and ser1 otherwise */
+		arg = MACH_IS_FALCON ? "ser2" : "ser1";
+
+	registered = !!atari_console_driver.write;
+	if (!strcmp(arg, "ser1")) {
+		/* ST-MFP Modem1 serial port */
+		atari_init_mfp_port(B9600|CS8);
+		atari_console_driver.write = atari_mfp_console_write;
+	} else if (!strcmp(arg, "ser2")) {
+		/* SCC Modem2 serial port */
+		atari_init_scc_port(B9600|CS8);
+		atari_console_driver.write = atari_scc_console_write;
+	} else if (!strcmp(arg, "midi")) {
+		/* MIDI port */
+		atari_init_midi_port(B9600|CS8);
+		atari_console_driver.write = atari_midi_console_write;
+	} else if (!strcmp(arg, "par")) {
+		/* parallel printer */
+		atari_turnoff_irq(IRQ_MFP_BUSY); /* avoid ints */
+		sound_ym.rd_data_reg_sel = 7;	/* select mixer control */
+		sound_ym.wd_data = 0xff;	/* sound off, ports are output */
+		sound_ym.rd_data_reg_sel = 15;	/* select port B */
+		sound_ym.wd_data = 0;		/* no char */
+		sound_ym.rd_data_reg_sel = 14;	/* select port A */
+		sound_ym.wd_data = sound_ym.rd_data_reg_sel | 0x20; /* strobe H */
+		atari_console_driver.write = atari_par_console_write;
+	}
+	if (atari_console_driver.write && !registered)
+		register_console(&atari_console_driver);
+
+	return 0;
+}
+
+early_param("debug", atari_debug_setup);