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[34.76.220.87]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b8f8b1bc81sm25677444f8f.69.2025.08.13.06.38.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 Aug 2025 06:38:40 -0700 (PDT) From: Ethan Graham To: ethangraham@google.com, glider@google.com Cc: andreyknvl@gmail.com, brendan.higgins@linux.dev, davidgow@google.com, dvyukov@google.com, jannh@google.com, elver@google.com, rmoar@google.com, shuah@kernel.org, tarasmadan@google.com, kasan-dev@googlegroups.com, kunit-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v1 RFC 3/6] kfuzztest: implement core module and input processing Date: Wed, 13 Aug 2025 13:38:09 +0000 Message-ID: <20250813133812.926145-4-ethan.w.s.graham@gmail.com> X-Mailer: git-send-email 2.51.0.rc0.205.g4a044479a3-goog In-Reply-To: <20250813133812.926145-1-ethan.w.s.graham@gmail.com> References: <20250813133812.926145-1-ethan.w.s.graham@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ethan Graham Add the core runtime implementation for KFuzzTest. This includes the module initialization, and the logic for receiving and processing user-provided inputs through debugfs. On module load, the framework discovers all test targets by iterating over the .kfuzztest_target section, creating a corresponding debugfs directory with a write-only 'input' file for each of them. Writing to an 'input' file triggers the main fuzzing sequence: 1. The serialized input is copied from userspace into a kernel buffer. 2. The buffer is parsed to validate the region array and relocation table. 3. Pointers are patched based on the relocation entries, and in KASAN builds the inter-region padding is poisoned. 4. The resulting struct is passed to the user-defined test logic. Signed-off-by: Ethan Graham --- lib/Makefile | 2 + lib/kfuzztest/Makefile | 4 + lib/kfuzztest/main.c | 161 +++++++++++++++++++++++++++++++ lib/kfuzztest/parse.c | 208 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 375 insertions(+) create mode 100644 lib/kfuzztest/Makefile create mode 100644 lib/kfuzztest/main.c create mode 100644 lib/kfuzztest/parse.c diff --git a/lib/Makefile b/lib/Makefile index c38582f187dd..511c44ef4b19 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -354,6 +354,8 @@ obj-$(CONFIG_GENERIC_LIB_CMPDI2) +=3D cmpdi2.o obj-$(CONFIG_GENERIC_LIB_UCMPDI2) +=3D ucmpdi2.o obj-$(CONFIG_OBJAGG) +=3D objagg.o =20 +obj-$(CONFIG_KFUZZTEST) +=3D kfuzztest/ + # pldmfw library obj-$(CONFIG_PLDMFW) +=3D pldmfw/ =20 diff --git a/lib/kfuzztest/Makefile b/lib/kfuzztest/Makefile new file mode 100644 index 000000000000..142d16007eea --- /dev/null +++ b/lib/kfuzztest/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0 + +obj-$(CONFIG_KFUZZTEST) +=3D kfuzztest.o +kfuzztest-objs :=3D main.o parse.o diff --git a/lib/kfuzztest/main.c b/lib/kfuzztest/main.c new file mode 100644 index 000000000000..fccda1319fb0 --- /dev/null +++ b/lib/kfuzztest/main.c @@ -0,0 +1,161 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * KFuzzTest core module initialization and debugfs interface. + * + * Copyright 2025 Google LLC + */ +#include +#include +#include +#include +#include + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Ethan Graham "); +MODULE_DESCRIPTION("Kernel Fuzz Testing Framework (KFuzzTest)"); + +extern const struct kfuzztest_target __kfuzztest_targets_start[]; +extern const struct kfuzztest_target __kfuzztest_targets_end[]; + +/** + * struct kfuzztest_dentry - A container for a debugfs dentry and its fops. + * @dentry: Pointer to the created debugfs dentry. + * @fops: The file_operations struct associated with this dentry. + * + * This simplifies state management by keeping a file's dentry and its + * operations bundled together. + */ +struct kfuzztest_dentry { + struct dentry *dentry; + struct file_operations fops; +}; + +/** + * struct kfuzztest_debugfs_state - Per-test-case debugfs state. + * @test_dir: The top-level debugfs directory for a single test case, e.g., + * /sys/kernel/debug/kfuzztest//. + * @input_dentry: The state for the "input" file, which is write-only. + * + * Wraps all debugfs components created for a single test case. + */ +struct kfuzztest_debugfs_state { + struct dentry *target_dir; + struct kfuzztest_dentry input_dentry; +}; + +/** + * struct kfuzztest_simple_fuzzer_state - Global state for the KFTF module. + * @kfuzztest_dir: The root debugfs directory, /sys/kernel/debug/kfuzztest= /. + * @debugfs_state: A statically sized array holding the state for each + * registered test case. + */ +struct kfuzztest_state { + struct file_operations fops; + struct dentry *kfuzztest_dir; + struct kfuzztest_debugfs_state *debugfs_state; +}; + +/* Global static variable to hold all state for the module. */ +static struct kfuzztest_state state; + +const umode_t KFUZZTEST_INPUT_PERMS =3D 0222; + +/** + * kfuzztest_init - Initializes the debug filesystem for KFuzzTest. + * + * Each registered test in the ".kfuzztest" section gets its own subdirect= ory + * under "/sys/kernel/debug/kfuzztest/" with one files: + * - input: write-only file to send input to the fuzz driver + * + * Returns: + * 0 on success. + * -ENODEV or other error codes if debugfs creation fails. + */ +static int __init kfuzztest_init(void) +{ + const struct kfuzztest_target *targ; + int ret =3D 0; + int i =3D 0; + size_t num_test_cases; + + num_test_cases =3D __kfuzztest_targets_end - __kfuzztest_targets_start; + + state.debugfs_state =3D + kzalloc(num_test_cases * sizeof(struct kfuzztest_debugfs_state), + GFP_KERNEL); + if (!state.debugfs_state) + return -ENOMEM; + + /* Create the main "kfuzztest" directory in /sys/kernel/debug. */ + state.kfuzztest_dir =3D debugfs_create_dir("kfuzztest", NULL); + if (!state.kfuzztest_dir) { + pr_warn("KFuzzTest: could not create debugfs"); + return -ENODEV; + } + + if (IS_ERR(state.kfuzztest_dir)) { + state.kfuzztest_dir =3D NULL; + return PTR_ERR(state.kfuzztest_dir); + } + + for (targ =3D __kfuzztest_targets_start; targ < __kfuzztest_targets_end; + targ++, i++) { + /* Create debugfs directory for the target. */ + state.debugfs_state[i].target_dir =3D + debugfs_create_dir(targ->name, state.kfuzztest_dir); + + if (!state.debugfs_state[i].target_dir) { + ret =3D -ENOMEM; + goto cleanup_failure; + } else if (IS_ERR(state.debugfs_state[i].target_dir)) { + ret =3D PTR_ERR(state.debugfs_state[i].target_dir); + goto cleanup_failure; + } + + /* Create an input file under the target's directory. */ + state.debugfs_state[i].input_dentry.fops =3D + (struct file_operations){ + .owner =3D THIS_MODULE, + .write =3D targ->write_input_cb, + }; + state.debugfs_state[i].input_dentry.dentry =3D + debugfs_create_file( + "input", KFUZZTEST_INPUT_PERMS, + state.debugfs_state[i].target_dir, NULL, + &state.debugfs_state[i].input_dentry.fops); + if (!state.debugfs_state[i].input_dentry.dentry) { + ret =3D -ENOMEM; + goto cleanup_failure; + } else if (IS_ERR(state.debugfs_state[i].input_dentry.dentry)) { + ret =3D PTR_ERR( + state.debugfs_state[i].input_dentry.dentry); + goto cleanup_failure; + } + + pr_info("KFuzzTest: registered target %s", targ->name); + } + + return 0; + +cleanup_failure: + debugfs_remove_recursive(state.kfuzztest_dir); + return ret; +} + +static void __exit kfuzztest_exit(void) +{ + pr_info("KFuzzTest: exiting"); + if (!state.kfuzztest_dir) + return; + + debugfs_remove_recursive(state.kfuzztest_dir); + state.kfuzztest_dir =3D NULL; + + if (state.debugfs_state) { + kfree(state.debugfs_state); + state.debugfs_state =3D NULL; + } +} + +module_init(kfuzztest_init); +module_exit(kfuzztest_exit); diff --git a/lib/kfuzztest/parse.c b/lib/kfuzztest/parse.c new file mode 100644 index 000000000000..6010171190ad --- /dev/null +++ b/lib/kfuzztest/parse.c @@ -0,0 +1,208 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * KFuzzTest input parsing and validation. + * + * Copyright 2025 Google LLC + */ +#include +#include + +/* + * Enforce a fixed struct size to ensure a consistent stride when iteratin= g over + * the array of these structs in the dedicated ELF section. + */ +static_assert(sizeof(struct kfuzztest_target) =3D=3D 32, "struct kfuzztest= _target should have size 32"); +static_assert(sizeof(struct kfuzztest_constraint) =3D=3D 64, "struct kfuzz= test_constraint should have size 64"); +static_assert(sizeof(struct kfuzztest_annotation) =3D=3D 32, "struct kfuzz= test_annotation should have size 32"); + +static int kfuzztest_relocate_v0(struct reloc_region_array *regions, struc= t reloc_table *rt, void *payload_start, + void *payload_end) +{ + struct reloc_region reg, src, dst; + void *poison_start, *poison_end; + uintptr_t *ptr_location; + struct reloc_entry re; + size_t i; + + /* Patch pointers. */ + for (i =3D 0; i < rt->num_entries; i++) { + re =3D rt->entries[i]; + src =3D regions->regions[re.region_id]; + ptr_location =3D (uintptr_t *)((char *)payload_start + src.offset + re.r= egion_offset); + if (re.value =3D=3D KFUZZTEST_REGIONID_NULL) + *ptr_location =3D (uintptr_t)NULL; + else if (re.value < regions->num_regions) { + dst =3D regions->regions[re.value]; + *ptr_location =3D (uintptr_t)((char *)payload_start + dst.offset); + } else + return -EINVAL; + } + + /* Poison the padding between regions. */ + for (i =3D 0; i < regions->num_regions; i++) { + reg =3D regions->regions[i]; + + /* Points to the beginning of the inter-region padding */ + poison_start =3D payload_start + reg.offset + reg.size; + if (i < regions->num_regions - 1) + poison_end =3D payload_start + regions->regions[i + 1].offset; + else + poison_end =3D payload_end; + + if ((char *)poison_end > (char *)payload_end) + return -EINVAL; + + kasan_poison_range(poison_start, poison_end - poison_start); + } + + /* Poison the padded area preceding the payload. */ + kasan_poison_range((char *)payload_start - rt->padding_size, rt->padding_= size); + return 0; +} + +static bool kfuzztest_input_is_valid(struct reloc_region_array *regions, s= truct reloc_table *rt, void *payload_start, + void *payload_end) +{ + size_t payload_size =3D (char *)payload_end - (char *)payload_start; + struct reloc_region reg, next_reg; + size_t usable_payload_size; + uint32_t region_end_offset; + struct reloc_entry reloc; + uint32_t i; + + if ((char *)payload_start > (char *)payload_end) + return false; + if (payload_size < KFUZZTEST_POISON_SIZE) + return false; + usable_payload_size =3D payload_size - KFUZZTEST_POISON_SIZE; + + for (i =3D 0; i < regions->num_regions; i++) { + reg =3D regions->regions[i]; + if (check_add_overflow(reg.offset, reg.size, ®ion_end_offset)) + return false; + if ((size_t)region_end_offset > usable_payload_size) + return false; + + if (i < regions->num_regions - 1) { + next_reg =3D regions->regions[i + 1]; + if (reg.offset > next_reg.offset) + return false; + /* + * Enforce the minimum poisonable gap between + * consecutive regions. + */ + if (reg.offset + reg.size + KFUZZTEST_POISON_SIZE > next_reg.offset) + return false; + } + } + + if (rt->padding_size < KFUZZTEST_POISON_SIZE) { + pr_info("validation failed because rt->padding_size =3D %u", rt->padding= _size); + return false; + } + + for (i =3D 0; i < rt->num_entries; i++) { + reloc =3D rt->entries[i]; + if (reloc.region_id >=3D regions->num_regions) + return false; + if (reloc.value !=3D KFUZZTEST_REGIONID_NULL && reloc.value >=3D regions= ->num_regions) + return false; + + reg =3D regions->regions[reloc.region_id]; + if (reloc.region_offset % (sizeof(uintptr_t)) || reloc.region_offset + s= izeof(uintptr_t) > reg.size) + return false; + } + + return true; +} + +static int kfuzztest_parse_input_v0(void *input, size_t input_size, struct= reloc_region_array **ret_regions, + struct reloc_table **ret_reloc_table, void **ret_payload_start, + void **ret_payload_end) +{ + size_t reloc_entries_size, reloc_regions_size; + size_t reloc_table_size, regions_size; + struct reloc_region_array *regions; + void *payload_end, *payload_start; + struct reloc_table *rt; + size_t curr_offset =3D 0; + + if (input_size < sizeof(struct reloc_region_array) + sizeof(struct reloc_= table)) + return -EINVAL; + + regions =3D input; + if (check_mul_overflow(regions->num_regions, sizeof(struct reloc_region),= &reloc_regions_size)) + return -EINVAL; + if (check_add_overflow(sizeof(*regions), reloc_regions_size, ®ions_siz= e)) + return -EINVAL; + + curr_offset =3D regions_size; + if (curr_offset > input_size) + return -EINVAL; + if (input_size - curr_offset < sizeof(struct reloc_table)) + return -EINVAL; + + rt =3D (struct reloc_table *)((char *)input + curr_offset); + + if (check_mul_overflow((size_t)rt->num_entries, sizeof(struct reloc_entry= ), &reloc_entries_size)) + return -EINVAL; + if (check_add_overflow(sizeof(*rt), reloc_entries_size, &reloc_table_size= )) + return -EINVAL; + if (check_add_overflow(reloc_table_size, rt->padding_size, &reloc_table_s= ize)) + return -EINVAL; + + if (check_add_overflow(curr_offset, reloc_table_size, &curr_offset)) + return -EINVAL; + if (curr_offset > input_size) + return -EINVAL; + + payload_start =3D (char *)input + curr_offset; + payload_end =3D (char *)input + input_size; + + if (!kfuzztest_input_is_valid(regions, rt, payload_start, payload_end)) + return -EINVAL; + + *ret_regions =3D regions; + *ret_reloc_table =3D rt; + *ret_payload_start =3D payload_start; + *ret_payload_end =3D payload_end; + return 0; +} + +static int kfuzztest_parse_and_relocate_v0(void *input, size_t input_size,= void **arg_ret) +{ + struct reloc_region_array *regions; + void *payload_start, *payload_end; + struct reloc_table *reloc_table; + int ret; + + ret =3D kfuzztest_parse_input_v0(input, input_size, ®ions, &reloc_tabl= e, &payload_start, &payload_end); + if (ret < 0) + return ret; + + ret =3D kfuzztest_relocate_v0(regions, reloc_table, payload_start, payloa= d_end); + if (ret < 0) + return ret; + *arg_ret =3D payload_start; + return 0; +} + +int kfuzztest_parse_and_relocate(void *input, size_t input_size, void **ar= g_ret) +{ + u32 version, magic; + + if (input_size < sizeof(u32) + sizeof(u32)) + return -EINVAL; + + magic =3D *(u32 *)input; + if (magic !=3D KFUZZTEST_HEADER_MAGIC) + return -EINVAL; + + version =3D *(u32 *)((char *)input + sizeof(u32)); + switch (version) { + case KFUZZTEST_V0: + return kfuzztest_parse_and_relocate_v0(input + sizeof(u64), input_size -= sizeof(u64), arg_ret); + } + + return -EINVAL; +} --=20 2.51.0.rc0.205.g4a044479a3-goog