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 --- Documentation/arch/powerpc/bootwrapper.rst | 131 +++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 Documentation/arch/powerpc/bootwrapper.rst (limited to 'Documentation/arch/powerpc/bootwrapper.rst') diff --git a/Documentation/arch/powerpc/bootwrapper.rst b/Documentation/arch/powerpc/bootwrapper.rst new file mode 100644 index 000000000..cdfa2bc84 --- /dev/null +++ b/Documentation/arch/powerpc/bootwrapper.rst @@ -0,0 +1,131 @@ +======================== +The PowerPC boot wrapper +======================== + +Copyright (C) Secret Lab Technologies Ltd. + +PowerPC image targets compresses and wraps the kernel image (vmlinux) with +a boot wrapper to make it usable by the system firmware. There is no +standard PowerPC firmware interface, so the boot wrapper is designed to +be adaptable for each kind of image that needs to be built. + +The boot wrapper can be found in the arch/powerpc/boot/ directory. The +Makefile in that directory has targets for all the available image types. +The different image types are used to support all of the various firmware +interfaces found on PowerPC platforms. OpenFirmware is the most commonly +used firmware type on general purpose PowerPC systems from Apple, IBM and +others. U-Boot is typically found on embedded PowerPC hardware, but there +are a handful of other firmware implementations which are also popular. Each +firmware interface requires a different image format. + +The boot wrapper is built from the makefile in arch/powerpc/boot/Makefile and +it uses the wrapper script (arch/powerpc/boot/wrapper) to generate target +image. The details of the build system is discussed in the next section. +Currently, the following image format targets exist: + + ==================== ======================================================== + cuImage.%: Backwards compatible uImage for older version of + U-Boot (for versions that don't understand the device + tree). This image embeds a device tree blob inside + the image. The boot wrapper, kernel and device tree + are all embedded inside the U-Boot uImage file format + with boot wrapper code that extracts data from the old + bd_info structure and loads the data into the device + tree before jumping into the kernel. + + Because of the series of #ifdefs found in the + bd_info structure used in the old U-Boot interfaces, + cuImages are platform specific. Each specific + U-Boot platform has a different platform init file + which populates the embedded device tree with data + from the platform specific bd_info file. The platform + specific cuImage platform init code can be found in + `arch/powerpc/boot/cuboot.*.c`. Selection of the correct + cuImage init code for a specific board can be found in + the wrapper structure. + + dtbImage.%: Similar to zImage, except device tree blob is embedded + inside the image instead of provided by firmware. The + output image file can be either an elf file or a flat + binary depending on the platform. + + dtbImages are used on systems which do not have an + interface for passing a device tree directly. + dtbImages are similar to simpleImages except that + dtbImages have platform specific code for extracting + data from the board firmware, but simpleImages do not + talk to the firmware at all. + + PlayStation 3 support uses dtbImage. So do Embedded + Planet boards using the PlanetCore firmware. Board + specific initialization code is typically found in a + file named arch/powerpc/boot/.c; but this + can be overridden by the wrapper script. + + simpleImage.%: Firmware independent compressed image that does not + depend on any particular firmware interface and embeds + a device tree blob. This image is a flat binary that + can be loaded to any location in RAM and jumped to. + Firmware cannot pass any configuration data to the + kernel with this image type and it depends entirely on + the embedded device tree for all information. + + treeImage.%; Image format for used with OpenBIOS firmware found + on some ppc4xx hardware. This image embeds a device + tree blob inside the image. + + uImage: Native image format used by U-Boot. The uImage target + does not add any boot code. It just wraps a compressed + vmlinux in the uImage data structure. This image + requires a version of U-Boot that is able to pass + a device tree to the kernel at boot. If using an older + version of U-Boot, then you need to use a cuImage + instead. + + zImage.%: Image format which does not embed a device tree. + Used by OpenFirmware and other firmware interfaces + which are able to supply a device tree. This image + expects firmware to provide the device tree at boot. + Typically, if you have general purpose PowerPC + hardware then you want this image format. + ==================== ======================================================== + +Image types which embed a device tree blob (simpleImage, dtbImage, treeImage, +and cuImage) all generate the device tree blob from a file in the +arch/powerpc/boot/dts/ directory. The Makefile selects the correct device +tree source based on the name of the target. Therefore, if the kernel is +built with 'make treeImage.walnut', then the build system will use +arch/powerpc/boot/dts/walnut.dts to build treeImage.walnut. + +Two special targets called 'zImage' and 'zImage.initrd' also exist. These +targets build all the default images as selected by the kernel configuration. +Default images are selected by the boot wrapper Makefile +(arch/powerpc/boot/Makefile) by adding targets to the $image-y variable. Look +at the Makefile to see which default image targets are available. + +How it is built +--------------- +arch/powerpc is designed to support multiplatform kernels, which means +that a single vmlinux image can be booted on many different target boards. +It also means that the boot wrapper must be able to wrap for many kinds of +images on a single build. The design decision was made to not use any +conditional compilation code (#ifdef, etc) in the boot wrapper source code. +All of the boot wrapper pieces are buildable at any time regardless of the +kernel configuration. Building all the wrapper bits on every kernel build +also ensures that obscure parts of the wrapper are at the very least compile +tested in a large variety of environments. + +The wrapper is adapted for different image types at link time by linking in +just the wrapper bits that are appropriate for the image type. The 'wrapper +script' (found in arch/powerpc/boot/wrapper) is called by the Makefile and +is responsible for selecting the correct wrapper bits for the image type. +The arguments are well documented in the script's comment block, so they +are not repeated here. However, it is worth mentioning that the script +uses the -p (platform) argument as the main method of deciding which wrapper +bits to compile in. Look for the large 'case "$platform" in' block in the +middle of the script. This is also the place where platform specific fixups +can be selected by changing the link order. + +In particular, care should be taken when working with cuImages. cuImage +wrapper bits are very board specific and care should be taken to make sure +the target you are trying to build is supported by the wrapper bits. -- cgit v1.3.1