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, 321 insertions, 0 deletions

diff --git a/arch/m68k/atari/time.c b/arch/m68k/atari/time.c
new file mode 100644
index 000000000..3453c6dc6
--- /dev/null
+++ b/arch/m68k/atari/time.c
@@ -0,0 +1,321 @@
+/*
+ * linux/arch/m68k/atari/time.c
+ *
+ * Atari time and real time clock 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/mc146818rtc.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/clocksource.h>
+#include <linux/delay.h>
+#include <linux/export.h>
+
+#include <asm/atariints.h>
+#include <asm/machdep.h>
+
+#include "atari.h"
+
+DEFINE_SPINLOCK(rtc_lock);
+EXPORT_SYMBOL_GPL(rtc_lock);
+
+static u64 atari_read_clk(struct clocksource *cs);
+
+static struct clocksource atari_clk = {
+	.name   = "mfp",
+	.rating = 100,
+	.read   = atari_read_clk,
+	.mask   = CLOCKSOURCE_MASK(32),
+	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+static u32 clk_total;
+static u8 last_timer_count;
+
+static irqreturn_t mfp_timer_c_handler(int irq, void *dev_id)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	do {
+		last_timer_count = st_mfp.tim_dt_c;
+	} while (last_timer_count == 1);
+	clk_total += INT_TICKS;
+	legacy_timer_tick(1);
+	timer_heartbeat();
+	local_irq_restore(flags);
+
+	return IRQ_HANDLED;
+}
+
+void __init
+atari_sched_init(void)
+{
+    /* set Timer C data Register */
+    st_mfp.tim_dt_c = INT_TICKS;
+    /* start timer C, div = 1:100 */
+    st_mfp.tim_ct_cd = (st_mfp.tim_ct_cd & 15) | 0x60;
+    /* install interrupt service routine for MFP Timer C */
+    if (request_irq(IRQ_MFP_TIMC, mfp_timer_c_handler, IRQF_TIMER, "timer",
+                    NULL))
+	pr_err("Couldn't register timer interrupt\n");
+
+    clocksource_register_hz(&atari_clk, INT_CLK);
+}
+
+/* ++andreas: gettimeoffset fixed to check for pending interrupt */
+
+static u64 atari_read_clk(struct clocksource *cs)
+{
+	unsigned long flags;
+	u8 count;
+	u32 ticks;
+
+	local_irq_save(flags);
+	/* Ensure that the count is monotonically decreasing, even though
+	 * the result may briefly stop changing after counter wrap-around.
+	 */
+	count = min(st_mfp.tim_dt_c, last_timer_count);
+	last_timer_count = count;
+
+	ticks = INT_TICKS - count;
+	ticks += clk_total;
+	local_irq_restore(flags);
+
+	return ticks;
+}
+
+
+static void mste_read(struct MSTE_RTC *val)
+{
+#define COPY(v) val->v=(mste_rtc.v & 0xf)
+	do {
+		COPY(sec_ones) ; COPY(sec_tens) ; COPY(min_ones) ;
+		COPY(min_tens) ; COPY(hr_ones) ; COPY(hr_tens) ;
+		COPY(weekday) ; COPY(day_ones) ; COPY(day_tens) ;
+		COPY(mon_ones) ; COPY(mon_tens) ; COPY(year_ones) ;
+		COPY(year_tens) ;
+	/* prevent from reading the clock while it changed */
+	} while (val->sec_ones != (mste_rtc.sec_ones & 0xf));
+#undef COPY
+}
+
+static void mste_write(struct MSTE_RTC *val)
+{
+#define COPY(v) mste_rtc.v=val->v
+	do {
+		COPY(sec_ones) ; COPY(sec_tens) ; COPY(min_ones) ;
+		COPY(min_tens) ; COPY(hr_ones) ; COPY(hr_tens) ;
+		COPY(weekday) ; COPY(day_ones) ; COPY(day_tens) ;
+		COPY(mon_ones) ; COPY(mon_tens) ; COPY(year_ones) ;
+		COPY(year_tens) ;
+	/* prevent from writing the clock while it changed */
+	} while (val->sec_ones != (mste_rtc.sec_ones & 0xf));
+#undef COPY
+}
+
+#define	RTC_READ(reg)				\
+    ({	unsigned char	__val;			\
+		(void) atari_writeb(reg,&tt_rtc.regsel);	\
+		__val = tt_rtc.data;		\
+		__val;				\
+	})
+
+#define	RTC_WRITE(reg,val)			\
+    do {					\
+		atari_writeb(reg,&tt_rtc.regsel);	\
+		tt_rtc.data = (val);		\
+	} while(0)
+
+
+#define HWCLK_POLL_INTERVAL	5
+
+int atari_mste_hwclk( int op, struct rtc_time *t )
+{
+    int hour, year;
+    int hr24=0;
+    struct MSTE_RTC val;
+
+    mste_rtc.mode=(mste_rtc.mode | 1);
+    hr24=mste_rtc.mon_tens & 1;
+    mste_rtc.mode=(mste_rtc.mode & ~1);
+
+    if (op) {
+        /* write: prepare values */
+
+        val.sec_ones = t->tm_sec % 10;
+        val.sec_tens = t->tm_sec / 10;
+        val.min_ones = t->tm_min % 10;
+        val.min_tens = t->tm_min / 10;
+        hour = t->tm_hour;
+        if (!hr24) {
+	    if (hour > 11)
+		hour += 20 - 12;
+	    if (hour == 0 || hour == 20)
+		hour += 12;
+        }
+        val.hr_ones = hour % 10;
+        val.hr_tens = hour / 10;
+        val.day_ones = t->tm_mday % 10;
+        val.day_tens = t->tm_mday / 10;
+        val.mon_ones = (t->tm_mon+1) % 10;
+        val.mon_tens = (t->tm_mon+1) / 10;
+        year = t->tm_year - 80;
+        val.year_ones = year % 10;
+        val.year_tens = year / 10;
+        val.weekday = t->tm_wday;
+        mste_write(&val);
+        mste_rtc.mode=(mste_rtc.mode | 1);
+        val.year_ones = (year % 4);	/* leap year register */
+        mste_rtc.mode=(mste_rtc.mode & ~1);
+    }
+    else {
+        mste_read(&val);
+        t->tm_sec = val.sec_ones + val.sec_tens * 10;
+        t->tm_min = val.min_ones + val.min_tens * 10;
+        hour = val.hr_ones + val.hr_tens * 10;
+	if (!hr24) {
+	    if (hour == 12 || hour == 12 + 20)
+		hour -= 12;
+	    if (hour >= 20)
+                hour += 12 - 20;
+        }
+	t->tm_hour = hour;
+	t->tm_mday = val.day_ones + val.day_tens * 10;
+        t->tm_mon  = val.mon_ones + val.mon_tens * 10 - 1;
+        t->tm_year = val.year_ones + val.year_tens * 10 + 80;
+        t->tm_wday = val.weekday;
+    }
+    return 0;
+}
+
+int atari_tt_hwclk( int op, struct rtc_time *t )
+{
+    int sec=0, min=0, hour=0, day=0, mon=0, year=0, wday=0;
+    unsigned long	flags;
+    unsigned char	ctrl;
+    int pm = 0;
+
+    ctrl = RTC_READ(RTC_CONTROL); /* control registers are
+                                   * independent from the UIP */
+
+    if (op) {
+        /* write: prepare values */
+
+        sec  = t->tm_sec;
+        min  = t->tm_min;
+        hour = t->tm_hour;
+        day  = t->tm_mday;
+        mon  = t->tm_mon + 1;
+        year = t->tm_year - atari_rtc_year_offset;
+        wday = t->tm_wday + (t->tm_wday >= 0);
+
+        if (!(ctrl & RTC_24H)) {
+	    if (hour > 11) {
+		pm = 0x80;
+		if (hour != 12)
+		    hour -= 12;
+	    }
+	    else if (hour == 0)
+		hour = 12;
+        }
+
+        if (!(ctrl & RTC_DM_BINARY)) {
+	    sec = bin2bcd(sec);
+	    min = bin2bcd(min);
+	    hour = bin2bcd(hour);
+	    day = bin2bcd(day);
+	    mon = bin2bcd(mon);
+	    year = bin2bcd(year);
+	    if (wday >= 0)
+		wday = bin2bcd(wday);
+        }
+    }
+
+    /* Reading/writing the clock registers is a bit critical due to
+     * the regular update cycle of the RTC. While an update is in
+     * progress, registers 0..9 shouldn't be touched.
+     * The problem is solved like that: If an update is currently in
+     * progress (the UIP bit is set), the process sleeps for a while
+     * (50ms). This really should be enough, since the update cycle
+     * normally needs 2 ms.
+     * If the UIP bit reads as 0, we have at least 244 usecs until the
+     * update starts. This should be enough... But to be sure,
+     * additionally the RTC_SET bit is set to prevent an update cycle.
+     */
+
+    while( RTC_READ(RTC_FREQ_SELECT) & RTC_UIP ) {
+	if (in_atomic() || irqs_disabled())
+	    mdelay(1);
+	else
+	    schedule_timeout_interruptible(HWCLK_POLL_INTERVAL);
+    }
+
+    local_irq_save(flags);
+    RTC_WRITE( RTC_CONTROL, ctrl | RTC_SET );
+    if (!op) {
+        sec  = RTC_READ( RTC_SECONDS );
+        min  = RTC_READ( RTC_MINUTES );
+        hour = RTC_READ( RTC_HOURS );
+        day  = RTC_READ( RTC_DAY_OF_MONTH );
+        mon  = RTC_READ( RTC_MONTH );
+        year = RTC_READ( RTC_YEAR );
+        wday = RTC_READ( RTC_DAY_OF_WEEK );
+    }
+    else {
+        RTC_WRITE( RTC_SECONDS, sec );
+        RTC_WRITE( RTC_MINUTES, min );
+        RTC_WRITE( RTC_HOURS, hour + pm);
+        RTC_WRITE( RTC_DAY_OF_MONTH, day );
+        RTC_WRITE( RTC_MONTH, mon );
+        RTC_WRITE( RTC_YEAR, year );
+        if (wday >= 0) RTC_WRITE( RTC_DAY_OF_WEEK, wday );
+    }
+    RTC_WRITE( RTC_CONTROL, ctrl & ~RTC_SET );
+    local_irq_restore(flags);
+
+    if (!op) {
+        /* read: adjust values */
+
+        if (hour & 0x80) {
+	    hour &= ~0x80;
+	    pm = 1;
+	}
+
+	if (!(ctrl & RTC_DM_BINARY)) {
+	    sec = bcd2bin(sec);
+	    min = bcd2bin(min);
+	    hour = bcd2bin(hour);
+	    day = bcd2bin(day);
+	    mon = bcd2bin(mon);
+	    year = bcd2bin(year);
+	    wday = bcd2bin(wday);
+        }
+
+        if (!(ctrl & RTC_24H)) {
+	    if (!pm && hour == 12)
+		hour = 0;
+	    else if (pm && hour != 12)
+		hour += 12;
+        }
+
+        t->tm_sec  = sec;
+        t->tm_min  = min;
+        t->tm_hour = hour;
+        t->tm_mday = day;
+        t->tm_mon  = mon - 1;
+        t->tm_year = year + atari_rtc_year_offset;
+        t->tm_wday = wday - 1;
+    }
+
+    return( 0 );
+}