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, 275 insertions, 0 deletions

diff --git a/drivers/firmware/efi/earlycon.c b/drivers/firmware/efi/earlycon.c
new file mode 100644
index 000000000..3d060d599
--- /dev/null
+++ b/drivers/firmware/efi/earlycon.c
@@ -0,0 +1,275 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2013 Intel Corporation; author Matt Fleming
+ */
+
+#include <linux/console.h>
+#include <linux/efi.h>
+#include <linux/font.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/serial_core.h>
+#include <linux/sysfb.h>
+#include <linux/string.h>
+
+#include <asm/early_ioremap.h>
+
+static const struct console *earlycon_console __initdata;
+static const struct font_desc *font;
+static u16 cur_line_y, max_line_y;
+static u32 efi_x_array[1024];
+static u32 efi_x, efi_y;
+static u64 fb_base;
+static bool fb_wb;
+static void *efi_fb;
+
+/*
+ * EFI earlycon needs to use early_memremap() to map the framebuffer.
+ * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
+ * memremap() should be used instead. memremap() will be available after
+ * paging_init() which is earlier than initcall callbacks. Thus adding this
+ * early initcall function early_efi_map_fb() to map the whole EFI framebuffer.
+ */
+static int __init efi_earlycon_remap_fb(void)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+
+	/* bail if there is no bootconsole or it was unregistered already */
+	if (!earlycon_console || !console_is_registered(earlycon_console))
+		return 0;
+
+	efi_fb = memremap(fb_base, si->lfb_size, fb_wb ? MEMREMAP_WB : MEMREMAP_WC);
+
+	return efi_fb ? 0 : -ENOMEM;
+}
+early_initcall(efi_earlycon_remap_fb);
+
+static int __init efi_earlycon_unmap_fb(void)
+{
+	/* unmap the bootconsole fb unless keep_bootcon left it registered */
+	if (efi_fb && !console_is_registered(earlycon_console))
+		memunmap(efi_fb);
+	return 0;
+}
+late_initcall(efi_earlycon_unmap_fb);
+
+static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
+{
+	pgprot_t fb_prot;
+
+	if (efi_fb)
+		return efi_fb + start;
+
+	fb_prot = fb_wb ? PAGE_KERNEL : pgprot_writecombine(PAGE_KERNEL);
+	return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
+}
+
+static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
+{
+	if (efi_fb)
+		return;
+
+	early_memunmap(addr, len);
+}
+
+static void efi_earlycon_clear_scanline(unsigned int y, const struct screen_info *si)
+{
+	unsigned long *dst;
+	u16 len;
+
+	len = si->lfb_linelength;
+	dst = efi_earlycon_map(y*len, len);
+	if (!dst)
+		return;
+
+	memset(dst, 0, len);
+	efi_earlycon_unmap(dst, len);
+}
+
+static void efi_earlycon_scroll_up(const struct screen_info *si)
+{
+	unsigned long *dst, *src;
+	u16 maxlen = 0;
+	u16 len;
+	u32 i, height;
+
+	/* Find the cached maximum x coordinate */
+	for (i = 0; i < max_line_y; i++) {
+		if (efi_x_array[i] > maxlen)
+			maxlen = efi_x_array[i];
+	}
+	maxlen *= 4;
+
+	len = si->lfb_linelength;
+	height = si->lfb_height;
+
+	for (i = 0; i < height - font->height; i++) {
+		dst = efi_earlycon_map(i*len, len);
+		if (!dst)
+			return;
+
+		src = efi_earlycon_map((i + font->height) * len, len);
+		if (!src) {
+			efi_earlycon_unmap(dst, len);
+			return;
+		}
+
+		memmove(dst, src, maxlen);
+
+		efi_earlycon_unmap(src, len);
+		efi_earlycon_unmap(dst, len);
+	}
+}
+
+static void efi_earlycon_write_char(u32 *dst, unsigned char c, unsigned int h,
+				    const struct screen_info *si)
+{
+	const u32 color_black = 0x00000000;
+	const u32 color_white = 0x00ffffff;
+	const u8 *src;
+	int m, n, bytes;
+	u8 x;
+
+	bytes = BITS_TO_BYTES(font->width);
+	src = font->data + c * font->height * bytes + h * bytes;
+
+	for (m = 0; m < font->width; m++) {
+		n = m % 8;
+		x = *(src + m / 8);
+		if ((x >> (7 - n)) & 1)
+			*dst = color_white;
+		else
+			*dst = color_black;
+		dst++;
+	}
+}
+
+static void
+efi_earlycon_write(struct console *con, const char *str, unsigned int num)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+	u32 cur_efi_x = efi_x;
+	unsigned int len;
+	const char *s;
+	void *dst;
+
+	len = si->lfb_linelength;
+
+	while (num) {
+		unsigned int linemax = (si->lfb_width - efi_x) / font->width;
+		unsigned int h, count;
+
+		count = strnchrnul(str, num, '\n') - str;
+		if (count > linemax)
+			count = linemax;
+
+		for (h = 0; h < font->height; h++) {
+			unsigned int n, x;
+
+			dst = efi_earlycon_map((efi_y + h) * len, len);
+			if (!dst)
+				return;
+
+			s = str;
+			n = count;
+			x = efi_x;
+
+			while (n-- > 0) {
+				efi_earlycon_write_char(dst + x * 4, *s, h, si);
+				x += font->width;
+				s++;
+			}
+
+			efi_earlycon_unmap(dst, len);
+		}
+
+		num -= count;
+		efi_x += count * font->width;
+		str += count;
+
+		if (num > 0 && *s == '\n') {
+			cur_efi_x = efi_x;
+			efi_x = 0;
+			efi_y += font->height;
+			str++;
+			num--;
+		}
+
+		if (efi_x + font->width > si->lfb_width) {
+			cur_efi_x = efi_x;
+			efi_x = 0;
+			efi_y += font->height;
+		}
+
+		if (efi_y + font->height > si->lfb_height) {
+			u32 i;
+
+			efi_x_array[cur_line_y] = cur_efi_x;
+			cur_line_y = (cur_line_y + 1) % max_line_y;
+
+			efi_y -= font->height;
+			efi_earlycon_scroll_up(si);
+
+			for (i = 0; i < font->height; i++)
+				efi_earlycon_clear_scanline(efi_y + i, si);
+		}
+	}
+}
+
+static bool __initdata fb_probed;
+
+void __init efi_earlycon_reprobe(void)
+{
+	if (fb_probed)
+		setup_earlycon("efifb");
+}
+
+static int __init efi_earlycon_setup(struct earlycon_device *device,
+				     const char *opt)
+{
+	const struct screen_info *si = &sysfb_primary_display.screen;
+	u16 xres, yres;
+	u32 i;
+
+	fb_wb = opt && !strcmp(opt, "ram");
+
+	if (si->orig_video_isVGA != VIDEO_TYPE_EFI) {
+		fb_probed = true;
+		return -ENODEV;
+	}
+
+	fb_base = si->lfb_base;
+	if (si->capabilities & VIDEO_CAPABILITY_64BIT_BASE)
+		fb_base |= (u64)si->ext_lfb_base << 32;
+
+	xres = si->lfb_width;
+	yres = si->lfb_height;
+
+	/*
+	 * efi_earlycon_write_char() implicitly assumes a framebuffer with
+	 * 32 bits per pixel.
+	 */
+	if (si->lfb_depth != 32)
+		return -ENODEV;
+
+	font = get_default_font(xres, yres, NULL, NULL);
+	if (!font)
+		return -ENODEV;
+
+	/* Fill the cache with maximum possible value of x coordinate */
+	memset32(efi_x_array, rounddown(xres, font->width), ARRAY_SIZE(efi_x_array));
+	efi_y = rounddown(yres, font->height);
+
+	/* Make sure we have cache for the x coordinate for the full screen */
+	max_line_y = efi_y / font->height + 1;
+	cur_line_y = 0;
+
+	efi_y -= font->height;
+	for (i = 0; i < (yres - efi_y) / font->height; i++)
+		efi_earlycon_scroll_up(si);
+
+	device->con->write = efi_earlycon_write;
+	earlycon_console = device->con;
+	return 0;
+}
+EARLYCON_DECLARE(efifb, efi_earlycon_setup);