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, 490 insertions, 0 deletions

diff --git a/drivers/video/vgastate.c b/drivers/video/vgastate.c
new file mode 100644
index 000000000..6a29d198f
--- /dev/null
+++ b/drivers/video/vgastate.c
@@ -0,0 +1,490 @@
+/*
+ * linux/drivers/video/vgastate.c -- VGA state save/restore
+ *
+ * Copyright 2002 James Simmons
+ *
+ * Copyright history from vga16fb.c:
+ *	Copyright 1999 Ben Pfaff and Petr Vandrovec
+ *	Based on VGA info at http://www.goodnet.com/~tinara/FreeVGA/home.htm
+ *	Based on VESA framebuffer (c) 1998 Gerd Knorr
+ *
+ * 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/module.h>
+#include <linux/slab.h>
+#include <linux/fb.h>
+#include <linux/vmalloc.h>
+#include <video/vga.h>
+
+struct regstate {
+	__u8 *vga_font0;
+	__u8 *vga_font1;
+	__u8 *vga_text;
+	__u8 *vga_cmap;
+	__u8 *attr;
+	__u8 *crtc;
+	__u8 *gfx;
+	__u8 *seq;
+	__u8 misc;
+};
+
+static inline unsigned char vga_rcrtcs(void __iomem *regbase, unsigned short iobase,
+				       unsigned char reg)
+{
+	vga_w(regbase, iobase + 0x4, reg);
+	return vga_r(regbase, iobase + 0x5);
+}
+
+static inline void vga_wcrtcs(void __iomem *regbase, unsigned short iobase,
+			      unsigned char reg, unsigned char val)
+{
+	vga_w(regbase, iobase + 0x4, reg);
+	vga_w(regbase, iobase + 0x5, val);
+}
+
+static void save_vga_text(struct vgastate *state, void __iomem *fbbase)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	int i;
+	u8 misc, attr10, gr4, gr5, gr6, seq1, seq2, seq4;
+	unsigned short iobase;
+
+	/* if in graphics mode, no need to save */
+	misc = vga_r(state->vgabase, VGA_MIS_R);
+	iobase = (misc & 1) ? 0x3d0 : 0x3b0;
+
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x00);
+	attr10 = vga_rattr(state->vgabase, 0x10);
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x20);
+
+	if (attr10 & 1)
+		return;
+
+	/* save regs */
+	gr4 = vga_rgfx(state->vgabase, VGA_GFX_PLANE_READ);
+	gr5 = vga_rgfx(state->vgabase, VGA_GFX_MODE);
+	gr6 = vga_rgfx(state->vgabase, VGA_GFX_MISC);
+	seq2 = vga_rseq(state->vgabase, VGA_SEQ_PLANE_WRITE);
+	seq4 = vga_rseq(state->vgabase, VGA_SEQ_MEMORY_MODE);
+
+	/* blank screen */
+	seq1 = vga_rseq(state->vgabase, VGA_SEQ_CLOCK_MODE);
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1 | 1 << 5);
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x3);
+
+	/* save font at plane 2 */
+	if (state->flags & VGA_SAVE_FONT0) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x4);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x2);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 4 * 8192; i++)
+			saved->vga_font0[i] = vga_r(fbbase, i);
+	}
+
+	/* save font at plane 3 */
+	if (state->flags & VGA_SAVE_FONT1) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x8);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x3);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < state->memsize; i++)
+			saved->vga_font1[i] = vga_r(fbbase, i);
+	}
+
+	/* save font at plane 0/1 */
+	if (state->flags & VGA_SAVE_TEXT) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x1);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 8192; i++)
+			saved->vga_text[i] = vga_r(fbbase, i);
+
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x2);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x1);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 8192; i++)
+			saved->vga_text[8192+i] = vga_r(fbbase + 2 * 8192, i);
+	}
+
+	/* restore regs */
+	vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, seq2);
+	vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, seq4);
+
+	vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, gr4);
+	vga_wgfx(state->vgabase, VGA_GFX_MODE, gr5);
+	vga_wgfx(state->vgabase, VGA_GFX_MISC, gr6);
+
+	/* unblank screen */
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1 & ~(1 << 5));
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x3);
+
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1);
+}
+
+static void restore_vga_text(struct vgastate *state, void __iomem *fbbase)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	int i;
+	u8 gr1, gr3, gr4, gr5, gr6, gr8;
+	u8 seq1, seq2, seq4;
+
+	/* save regs */
+	gr1 = vga_rgfx(state->vgabase, VGA_GFX_SR_ENABLE);
+	gr3 = vga_rgfx(state->vgabase, VGA_GFX_DATA_ROTATE);
+	gr4 = vga_rgfx(state->vgabase, VGA_GFX_PLANE_READ);
+	gr5 = vga_rgfx(state->vgabase, VGA_GFX_MODE);
+	gr6 = vga_rgfx(state->vgabase, VGA_GFX_MISC);
+	gr8 = vga_rgfx(state->vgabase, VGA_GFX_BIT_MASK);
+	seq2 = vga_rseq(state->vgabase, VGA_SEQ_PLANE_WRITE);
+	seq4 = vga_rseq(state->vgabase, VGA_SEQ_MEMORY_MODE);
+
+	/* blank screen */
+	seq1 = vga_rseq(state->vgabase, VGA_SEQ_CLOCK_MODE);
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1 | 1 << 5);
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x3);
+
+	if (state->depth == 4) {
+		vga_wgfx(state->vgabase, VGA_GFX_DATA_ROTATE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_BIT_MASK, 0xff);
+		vga_wgfx(state->vgabase, VGA_GFX_SR_ENABLE, 0x00);
+	}
+
+	/* restore font at plane 2 */
+	if (state->flags & VGA_SAVE_FONT0) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x4);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x2);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 4 * 8192; i++)
+			vga_w(fbbase, i, saved->vga_font0[i]);
+	}
+
+	/* restore font at plane 3 */
+	if (state->flags & VGA_SAVE_FONT1) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x8);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x3);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < state->memsize; i++)
+			vga_w(fbbase, i, saved->vga_font1[i]);
+	}
+
+	/* restore font at plane 0/1 */
+	if (state->flags & VGA_SAVE_TEXT) {
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x1);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 8192; i++)
+			vga_w(fbbase, i, saved->vga_text[i]);
+
+		vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, 0x2);
+		vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, 0x6);
+		vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, 0x1);
+		vga_wgfx(state->vgabase, VGA_GFX_MODE, 0x0);
+		vga_wgfx(state->vgabase, VGA_GFX_MISC, 0x5);
+		for (i = 0; i < 8192; i++)
+			vga_w(fbbase, i, saved->vga_text[8192+i]);
+	}
+
+	/* unblank screen */
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x1);
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1 & ~(1 << 5));
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x3);
+
+	/* restore regs */
+	vga_wgfx(state->vgabase, VGA_GFX_SR_ENABLE, gr1);
+	vga_wgfx(state->vgabase, VGA_GFX_DATA_ROTATE, gr3);
+	vga_wgfx(state->vgabase, VGA_GFX_PLANE_READ, gr4);
+	vga_wgfx(state->vgabase, VGA_GFX_MODE, gr5);
+	vga_wgfx(state->vgabase, VGA_GFX_MISC, gr6);
+	vga_wgfx(state->vgabase, VGA_GFX_BIT_MASK, gr8);
+
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE, seq1);
+	vga_wseq(state->vgabase, VGA_SEQ_PLANE_WRITE, seq2);
+	vga_wseq(state->vgabase, VGA_SEQ_MEMORY_MODE, seq4);
+}
+
+static void save_vga_mode(struct vgastate *state)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	unsigned short iobase;
+	int i;
+
+	saved->misc = vga_r(state->vgabase, VGA_MIS_R);
+	if (saved->misc & 1)
+		iobase = 0x3d0;
+	else
+		iobase = 0x3b0;
+
+	for (i = 0; i < state->num_crtc; i++)
+		saved->crtc[i] = vga_rcrtcs(state->vgabase, iobase, i);
+
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x00);
+	for (i = 0; i < state->num_attr; i++) {
+		vga_r(state->vgabase, iobase + 0xa);
+		saved->attr[i] = vga_rattr(state->vgabase, i);
+	}
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x20);
+
+	for (i = 0; i < state->num_gfx; i++)
+		saved->gfx[i] = vga_rgfx(state->vgabase, i);
+
+	for (i = 0; i < state->num_seq; i++)
+		saved->seq[i] = vga_rseq(state->vgabase, i);
+}
+
+static void restore_vga_mode(struct vgastate *state)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	unsigned short iobase;
+	int i;
+
+	vga_w(state->vgabase, VGA_MIS_W, saved->misc);
+
+	if (saved->misc & 1)
+		iobase = 0x3d0;
+	else
+		iobase = 0x3b0;
+
+	/* turn off display */
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE,
+		 saved->seq[VGA_SEQ_CLOCK_MODE] | 0x20);
+
+	/* disable sequencer */
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x01);
+
+	/* enable palette addressing */
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x00);
+
+	for (i = 2; i < state->num_seq; i++)
+		vga_wseq(state->vgabase, i, saved->seq[i]);
+
+
+	/* unprotect vga regs */
+	vga_wcrtcs(state->vgabase, iobase, 17, saved->crtc[17] & ~0x80);
+	for (i = 0; i < state->num_crtc; i++)
+		vga_wcrtcs(state->vgabase, iobase, i, saved->crtc[i]);
+
+	for (i = 0; i < state->num_gfx; i++)
+		vga_wgfx(state->vgabase, i, saved->gfx[i]);
+
+	for (i = 0; i < state->num_attr; i++) {
+		vga_r(state->vgabase, iobase + 0xa);
+		vga_wattr(state->vgabase, i, saved->attr[i]);
+	}
+
+	/* reenable sequencer */
+	vga_wseq(state->vgabase, VGA_SEQ_RESET, 0x03);
+	/* turn display on */
+	vga_wseq(state->vgabase, VGA_SEQ_CLOCK_MODE,
+		 saved->seq[VGA_SEQ_CLOCK_MODE] & ~(1 << 5));
+
+	/* disable video/palette source */
+	vga_r(state->vgabase, iobase + 0xa);
+	vga_w(state->vgabase, VGA_ATT_W, 0x20);
+}
+
+static void save_vga_cmap(struct vgastate *state)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	int i;
+
+	vga_w(state->vgabase, VGA_PEL_MSK, 0xff);
+
+	/* assumes DAC is readable and writable */
+	vga_w(state->vgabase, VGA_PEL_IR, 0x00);
+	for (i = 0; i < 768; i++)
+		saved->vga_cmap[i] = vga_r(state->vgabase, VGA_PEL_D);
+}
+
+static void restore_vga_cmap(struct vgastate *state)
+{
+	struct regstate *saved = (struct regstate *) state->vidstate;
+	int i;
+
+	vga_w(state->vgabase, VGA_PEL_MSK, 0xff);
+
+	/* assumes DAC is readable and writable */
+	vga_w(state->vgabase, VGA_PEL_IW, 0x00);
+	for (i = 0; i < 768; i++)
+		vga_w(state->vgabase, VGA_PEL_D, saved->vga_cmap[i]);
+}
+
+static void vga_cleanup(struct vgastate *state)
+{
+	if (state->vidstate != NULL) {
+		struct regstate *saved = (struct regstate *) state->vidstate;
+
+		vfree(saved->vga_font0);
+		vfree(saved->vga_font1);
+		vfree(saved->vga_text);
+		vfree(saved->vga_cmap);
+		vfree(saved->attr);
+		kfree(saved);
+		state->vidstate = NULL;
+	}
+}
+
+int save_vga(struct vgastate *state)
+{
+	struct regstate *saved;
+
+	saved = kzalloc_obj(struct regstate);
+
+	if (saved == NULL)
+		return 1;
+
+	state->vidstate = (void *)saved;
+
+	if (state->flags & VGA_SAVE_CMAP) {
+		saved->vga_cmap = vmalloc(768);
+		if (!saved->vga_cmap) {
+			vga_cleanup(state);
+			return 1;
+		}
+		save_vga_cmap(state);
+	}
+
+	if (state->flags & VGA_SAVE_MODE) {
+		int total;
+
+		if (state->num_attr < 21)
+			state->num_attr = 21;
+		if (state->num_crtc < 25)
+			state->num_crtc = 25;
+		if (state->num_gfx < 9)
+			state->num_gfx = 9;
+		if (state->num_seq < 5)
+			state->num_seq = 5;
+		total = state->num_attr + state->num_crtc +
+			state->num_gfx + state->num_seq;
+
+		saved->attr = vmalloc(total);
+		if (!saved->attr) {
+			vga_cleanup(state);
+			return 1;
+		}
+		saved->crtc = saved->attr + state->num_attr;
+		saved->gfx = saved->crtc + state->num_crtc;
+		saved->seq = saved->gfx + state->num_gfx;
+
+		save_vga_mode(state);
+	}
+
+	if (state->flags & VGA_SAVE_FONTS) {
+		void __iomem *fbbase;
+
+		/* exit if window is less than 32K */
+		if (state->memsize && state->memsize < 4 * 8192) {
+			vga_cleanup(state);
+			return 1;
+		}
+		if (!state->memsize)
+			state->memsize = 8 * 8192;
+
+		if (!state->membase)
+			state->membase = 0xA0000;
+
+		fbbase = ioremap(state->membase, state->memsize);
+
+		if (!fbbase) {
+			vga_cleanup(state);
+			return 1;
+		}
+
+		/*
+		 * save only first 32K used by vgacon
+		 */
+		if (state->flags & VGA_SAVE_FONT0) {
+			saved->vga_font0 = vmalloc(4 * 8192);
+			if (!saved->vga_font0) {
+				iounmap(fbbase);
+				vga_cleanup(state);
+				return 1;
+			}
+		}
+		/*
+		 * largely unused, but if required by the caller
+		 * we'll just save everything.
+		 */
+		if (state->flags & VGA_SAVE_FONT1) {
+			saved->vga_font1 = vmalloc(state->memsize);
+			if (!saved->vga_font1) {
+				iounmap(fbbase);
+				vga_cleanup(state);
+				return 1;
+			}
+		}
+		/*
+		 * Save 8K at plane0[0], and 8K at plane1[16K]
+		 */
+		if (state->flags & VGA_SAVE_TEXT) {
+			saved->vga_text = vmalloc(8192 * 2);
+			if (!saved->vga_text) {
+				iounmap(fbbase);
+				vga_cleanup(state);
+				return 1;
+			}
+		}
+
+		save_vga_text(state, fbbase);
+		iounmap(fbbase);
+	}
+	return 0;
+}
+
+int restore_vga(struct vgastate *state)
+{
+	if (state->vidstate == NULL)
+		return 1;
+
+	if (state->flags & VGA_SAVE_MODE)
+		restore_vga_mode(state);
+
+	if (state->flags & VGA_SAVE_FONTS) {
+		void __iomem *fbbase = ioremap(state->membase, state->memsize);
+
+		if (!fbbase) {
+			vga_cleanup(state);
+			return 1;
+		}
+		restore_vga_text(state, fbbase);
+		iounmap(fbbase);
+	}
+
+	if (state->flags & VGA_SAVE_CMAP)
+		restore_vga_cmap(state);
+
+	vga_cleanup(state);
+	return 0;
+}
+
+EXPORT_SYMBOL(save_vga);
+EXPORT_SYMBOL(restore_vga);
+
+MODULE_AUTHOR("James Simmons <jsimmons@users.sf.net>");
+MODULE_DESCRIPTION("VGA State Save/Restore");
+MODULE_LICENSE("GPL");
+