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/crypto/api-intro.rst | 262 +++++++++++++++++++++++++++++++++++++ 1 file changed, 262 insertions(+) create mode 100644 Documentation/crypto/api-intro.rst (limited to 'Documentation/crypto/api-intro.rst') diff --git a/Documentation/crypto/api-intro.rst b/Documentation/crypto/api-intro.rst new file mode 100644 index 000000000..15201be0b --- /dev/null +++ b/Documentation/crypto/api-intro.rst @@ -0,0 +1,262 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================= +Scatterlist Cryptographic API +============================= + +Introduction +============ + +The Scatterlist Crypto API takes page vectors (scatterlists) as +arguments, and works directly on pages. In some cases (e.g. ECB +mode ciphers), this will allow for pages to be encrypted in-place +with no copying. + +One of the initial goals of this design was to readily support IPsec, +so that processing can be applied to paged skb's without the need +for linearization. + + +Details +======= + +At the lowest level are algorithms, which register dynamically with the +API. + +'Transforms' are user-instantiated objects, which maintain state, handle all +of the implementation logic (e.g. manipulating page vectors) and provide an +abstraction to the underlying algorithms. However, at the user +level they are very simple. + +Conceptually, the API layering looks like this:: + + [transform api] (user interface) + [transform ops] (per-type logic glue e.g. cipher.c, compress.c) + [algorithm api] (for registering algorithms) + +The idea is to make the user interface and algorithm registration API +very simple, while hiding the core logic from both. Many good ideas +from existing APIs such as Cryptoapi and Nettle have been adapted for this. + +The API currently supports five main types of transforms: AEAD (Authenticated +Encryption with Associated Data), Block Ciphers, Ciphers, Compressors and +Hashes. + +Please note that Block Ciphers is somewhat of a misnomer. It is in fact +meant to support all ciphers including stream ciphers. The difference +between Block Ciphers and Ciphers is that the latter operates on exactly +one block while the former can operate on an arbitrary amount of data, +subject to block size requirements (i.e., non-stream ciphers can only +process multiples of blocks). + +Here's an example of how to use the API:: + + #include + #include + #include + + struct scatterlist sg[2]; + char result[128]; + struct crypto_ahash *tfm; + struct ahash_request *req; + + tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC); + if (IS_ERR(tfm)) + fail(); + + /* ... set up the scatterlists ... */ + + req = ahash_request_alloc(tfm, GFP_ATOMIC); + if (!req) + fail(); + + ahash_request_set_callback(req, 0, NULL, NULL); + ahash_request_set_crypt(req, sg, result, 2); + + if (crypto_ahash_digest(req)) + fail(); + + ahash_request_free(req); + crypto_free_ahash(tfm); + + +Many real examples are available in the regression test module (tcrypt.c). + + +Developer Notes +=============== + +Transforms may only be allocated in user context, and cryptographic +methods may only be called from softirq and user contexts. For +transforms with a setkey method it too should only be called from +user context. + +When using the API for ciphers, performance will be optimal if each +scatterlist contains data which is a multiple of the cipher's block +size (typically 8 bytes). This prevents having to do any copying +across non-aligned page fragment boundaries. + + +Adding New Algorithms +===================== + +When submitting a new algorithm for inclusion, a mandatory requirement +is that at least a few test vectors from known sources (preferably +standards) be included. + +Converting existing well known code is preferred, as it is more likely +to have been reviewed and widely tested. If submitting code from LGPL +sources, please consider changing the license to GPL (see section 3 of +the LGPL). + +Algorithms submitted must also be generally patent-free (e.g. IDEA +will not be included in the mainline until around 2011), and be based +on a recognized standard and/or have been subjected to appropriate +peer review. + +Also check for any RFCs which may relate to the use of specific algorithms, +as well as general application notes such as RFC2451 ("The ESP CBC-Mode +Cipher Algorithms"). + +It's a good idea to avoid using lots of macros and use inlined functions +instead, as gcc does a good job with inlining, while excessive use of +macros can cause compilation problems on some platforms. + +Also check the TODO list at the web site listed below to see what people +might already be working on. + + +Bugs +==== + +Send bug reports to: + linux-crypto@vger.kernel.org + +Cc: + Herbert Xu , + David S. Miller + + +Further Information +=================== + +For further patches and various updates, including the current TODO +list, see: +http://gondor.apana.org.au/~herbert/crypto/ + + +Authors +======= + +- James Morris +- David S. Miller +- Herbert Xu + + +Credits +======= + +The following people provided invaluable feedback during the development +of the API: + + - Alexey Kuznetzov + - Rusty Russell + - Herbert Valerio Riedel + - Jeff Garzik + - Michael Richardson + - Andrew Morton + - Ingo Oeser + - Christoph Hellwig + +Portions of this API were derived from the following projects: + + Kerneli Cryptoapi (http://www.kerneli.org/) + - Alexander Kjeldaas + - Herbert Valerio Riedel + - Kyle McMartin + - Jean-Luc Cooke + - David Bryson + - Clemens Fruhwirth + - Tobias Ringstrom + - Harald Welte + +and; + + Nettle (https://www.lysator.liu.se/~nisse/nettle/) + - Niels Möller + +Original developers of the crypto algorithms: + + - Dana L. How (DES) + - Andrew Tridgell and Steve French (MD4) + - Colin Plumb (MD5) + - Steve Reid (SHA1) + - Jean-Luc Cooke (SHA256, SHA384, SHA512) + - Kazunori Miyazawa / USAGI (HMAC) + - Matthew Skala (Twofish) + - Dag Arne Osvik (Serpent) + - Brian Gladman (AES) + - Kartikey Mahendra Bhatt (CAST6) + - Jon Oberheide (ARC4) + - Jouni Malinen (Michael MIC) + - NTT(Nippon Telegraph and Telephone Corporation) (Camellia) + +SHA1 algorithm contributors: + - Jean-Francois Dive + +DES algorithm contributors: + - Raimar Falke + - Gisle Sælensminde + - Niels Möller + +Blowfish algorithm contributors: + - Herbert Valerio Riedel + - Kyle McMartin + +Twofish algorithm contributors: + - Werner Koch + - Marc Mutz + +SHA256/384/512 algorithm contributors: + - Andrew McDonald + - Kyle McMartin + - Herbert Valerio Riedel + +AES algorithm contributors: + - Alexander Kjeldaas + - Herbert Valerio Riedel + - Kyle McMartin + - Adam J. Richter + - Fruhwirth Clemens (i586) + - Linus Torvalds (i586) + +CAST5 algorithm contributors: + - Kartikey Mahendra Bhatt (original developers unknown, FSF copyright). + +TEA/XTEA algorithm contributors: + - Aaron Grothe + - Michael Ringe + +Khazad algorithm contributors: + - Aaron Grothe + +Whirlpool algorithm contributors: + - Aaron Grothe + - Jean-Luc Cooke + +Anubis algorithm contributors: + - Aaron Grothe + +Tiger algorithm contributors: + - Aaron Grothe + +VIA PadLock contributors: + - Michal Ludvig + +Camellia algorithm contributors: + - NTT(Nippon Telegraph and Telephone Corporation) (Camellia) + +Generic scatterwalk code by Adam J. Richter + +Please send any credits updates or corrections to: +Herbert Xu -- cgit v1.3.1