From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- arch/powerpc/boot/ugecon.c | 142 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+) create mode 100644 arch/powerpc/boot/ugecon.c (limited to 'arch/powerpc/boot/ugecon.c') diff --git a/arch/powerpc/boot/ugecon.c b/arch/powerpc/boot/ugecon.c new file mode 100644 index 000000000..938a38bd4 --- /dev/null +++ b/arch/powerpc/boot/ugecon.c @@ -0,0 +1,142 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * arch/powerpc/boot/ugecon.c + * + * USB Gecko bootwrapper console. + * Copyright (C) 2008-2009 The GameCube Linux Team + * Copyright (C) 2008,2009 Albert Herranz + */ + +#include +#include "stdio.h" +#include "types.h" +#include "io.h" +#include "ops.h" + + +#define EXI_CLK_32MHZ 5 + +#define EXI_CSR 0x00 +#define EXI_CSR_CLKMASK (0x7<<4) +#define EXI_CSR_CLK_32MHZ (EXI_CLK_32MHZ<<4) +#define EXI_CSR_CSMASK (0x7<<7) +#define EXI_CSR_CS_0 (0x1<<7) /* Chip Select 001 */ + +#define EXI_CR 0x0c +#define EXI_CR_TSTART (1<<0) +#define EXI_CR_WRITE (1<<2) +#define EXI_CR_READ_WRITE (2<<2) +#define EXI_CR_TLEN(len) (((len)-1)<<4) + +#define EXI_DATA 0x10 + + +/* virtual address base for input/output, retrieved from device tree */ +static void *ug_io_base; + + +static u32 ug_io_transaction(u32 in) +{ + u32 *csr_reg = ug_io_base + EXI_CSR; + u32 *data_reg = ug_io_base + EXI_DATA; + u32 *cr_reg = ug_io_base + EXI_CR; + u32 csr, data, cr; + + /* select */ + csr = EXI_CSR_CLK_32MHZ | EXI_CSR_CS_0; + out_be32(csr_reg, csr); + + /* read/write */ + data = in; + out_be32(data_reg, data); + cr = EXI_CR_TLEN(2) | EXI_CR_READ_WRITE | EXI_CR_TSTART; + out_be32(cr_reg, cr); + + while (in_be32(cr_reg) & EXI_CR_TSTART) + barrier(); + + /* deselect */ + out_be32(csr_reg, 0); + + data = in_be32(data_reg); + return data; +} + +static int ug_is_txfifo_ready(void) +{ + return ug_io_transaction(0xc0000000) & 0x04000000; +} + +static void ug_raw_putc(char ch) +{ + ug_io_transaction(0xb0000000 | (ch << 20)); +} + +static void ug_putc(char ch) +{ + int count = 16; + + if (!ug_io_base) + return; + + while (!ug_is_txfifo_ready() && count--) + barrier(); + if (count >= 0) + ug_raw_putc(ch); +} + +void ug_console_write(const char *buf, int len) +{ + char *b = (char *)buf; + + while (len--) { + if (*b == '\n') + ug_putc('\r'); + ug_putc(*b++); + } +} + +static int ug_is_adapter_present(void) +{ + if (!ug_io_base) + return 0; + return ug_io_transaction(0x90000000) == 0x04700000; +} + +static void *ug_grab_exi_io_base(void) +{ + u32 v; + void *devp; + + devp = find_node_by_compatible(NULL, "nintendo,flipper-exi"); + if (devp == NULL) + goto err_out; + if (getprop(devp, "virtual-reg", &v, sizeof(v)) != sizeof(v)) + goto err_out; + + return (void *)v; + +err_out: + return NULL; +} + +void *ug_probe(void) +{ + void *exi_io_base; + int i; + + exi_io_base = ug_grab_exi_io_base(); + if (!exi_io_base) + return NULL; + + /* look for a usbgecko on memcard slots A and B */ + for (i = 0; i < 2; i++) { + ug_io_base = exi_io_base + 0x14 * i; + if (ug_is_adapter_present()) + break; + } + if (i == 2) + ug_io_base = NULL; + return ug_io_base; +} + -- cgit v1.3.1