| Message ID | 20231103214535.2674059-6-song@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | bpf: File verification with LSM and fsverity | expand |
On Fri, Nov 3, 2023 at 2:46 PM Song Liu <song@kernel.org> wrote: > > fsverity provides fast and reliable hash of files, namely fsverity_digest. > The digest can be used by security solutions to verify file contents. > > Add new kfunc bpf_get_fsverity_digest() so that we can access fsverity from > BPF LSM programs. This kfunc is added to fs/verity/measure.c because some > data structure used in the function is private to fsverity > (fs/verity/fsverity_private.h). > > To avoid recursion, bpf_get_fsverity_digest is only allowed in BPF LSM > programs. > > Signed-off-by: Song Liu <song@kernel.org> > Acked-by: Eric Biggers <ebiggers@google.com> > --- > fs/verity/fsverity_private.h | 10 +++++ > fs/verity/init.c | 1 + > fs/verity/measure.c | 85 ++++++++++++++++++++++++++++++++++++ > 3 files changed, 96 insertions(+) > > diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h > index d071a6e32581..a6a6b2749241 100644 > --- a/fs/verity/fsverity_private.h > +++ b/fs/verity/fsverity_private.h > @@ -100,6 +100,16 @@ fsverity_msg(const struct inode *inode, const char *level, > #define fsverity_err(inode, fmt, ...) \ > fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) > > +/* measure.c */ > + > +#ifdef CONFIG_BPF_SYSCALL > +void __init fsverity_init_bpf(void); > +#else > +static inline void fsverity_init_bpf(void) > +{ > +} > +#endif > + > /* open.c */ > > int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, > diff --git a/fs/verity/init.c b/fs/verity/init.c > index a29f062f6047..1e207c0f71de 100644 > --- a/fs/verity/init.c > +++ b/fs/verity/init.c > @@ -69,6 +69,7 @@ static int __init fsverity_init(void) > fsverity_init_workqueue(); > fsverity_init_sysctl(); > fsverity_init_signature(); > + fsverity_init_bpf(); > return 0; > } > late_initcall(fsverity_init) > diff --git a/fs/verity/measure.c b/fs/verity/measure.c > index eec5956141da..a08177eda96e 100644 > --- a/fs/verity/measure.c > +++ b/fs/verity/measure.c > @@ -7,6 +7,8 @@ > > #include "fsverity_private.h" > > +#include <linux/bpf.h> > +#include <linux/btf.h> > #include <linux/uaccess.h> > > /** > @@ -100,3 +102,86 @@ int fsverity_get_digest(struct inode *inode, > return hash_alg->digest_size; > } > EXPORT_SYMBOL_GPL(fsverity_get_digest); > + > +#ifdef CONFIG_BPF_SYSCALL > + > +/* bpf kfuncs */ > +__diag_push(); > +__diag_ignore_all("-Wmissing-prototypes", > + "kfuncs which will be used in BPF programs"); > + same as in previous patch, we have dedicated macros for this, please use them > +/** > + * bpf_get_fsverity_digest: read fsverity digest of file > + * @file: file to get digest from > + * @digest_ptr: (out) dynptr for struct fsverity_digest > + * > + * Read fsverity_digest of *file* into *digest_ptr*. > + * > + * Return: 0 on success, a negative value on error. > + */ > +__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr) > +{ > + const struct inode *inode = file_inode(file); > + struct fsverity_digest *arg; > + const struct fsverity_info *vi; > + const struct fsverity_hash_alg *hash_alg; > + int out_digest_sz; > + > + arg = __bpf_dynptr_data_rw(digest_ptr, __bpf_dynptr_size(digest_ptr)); > + if (!arg) > + return -EINVAL; > + > + if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) > + return -EINVAL; > + > + if (__bpf_dynptr_size(digest_ptr) < sizeof(struct fsverity_digest)) > + return -EINVAL; > + similar nit, you call __bpf_dynptr_size(digest_ptr) many times, let's use `u32 len = __bpf_dynptr_size(digest_ptr);` ? > + vi = fsverity_get_info(inode); > + if (!vi) > + return -ENODATA; /* not a verity file */ > + > + hash_alg = vi->tree_params.hash_alg; > + > + arg->digest_algorithm = hash_alg - fsverity_hash_algs; > + arg->digest_size = hash_alg->digest_size; > + > + out_digest_sz = __bpf_dynptr_size(digest_ptr) - sizeof(struct fsverity_digest); > + > + /* copy digest */ > + memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); > + > + /* fill the extra buffer with zeros */ > + if (out_digest_sz > hash_alg->digest_size) > + memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); > + > + return 0; > +} > + > +__diag_pop(); > + > +BTF_SET8_START(fsverity_set_ids) > +BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) > +BTF_SET8_END(fsverity_set_ids) > + > +static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) > +{ > + if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id)) > + return 0; > + > + /* Only allow to attach from LSM hooks, to avoid recursion */ > + return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; > +} > + > +static const struct btf_kfunc_id_set bpf_fsverity_set = { > + .owner = THIS_MODULE, > + .set = &fsverity_set_ids, > + .filter = bpf_get_fsverity_digest_filter, > +}; > + > +void __init fsverity_init_bpf(void) > +{ > + register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); > +} > + > +#endif /* CONFIG_BPF_SYSCALL */ > -- > 2.34.1 >
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index d071a6e32581..a6a6b2749241 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -100,6 +100,16 @@ fsverity_msg(const struct inode *inode, const char *level, #define fsverity_err(inode, fmt, ...) \ fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) +/* measure.c */ + +#ifdef CONFIG_BPF_SYSCALL +void __init fsverity_init_bpf(void); +#else +static inline void fsverity_init_bpf(void) +{ +} +#endif + /* open.c */ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params, diff --git a/fs/verity/init.c b/fs/verity/init.c index a29f062f6047..1e207c0f71de 100644 --- a/fs/verity/init.c +++ b/fs/verity/init.c @@ -69,6 +69,7 @@ static int __init fsverity_init(void) fsverity_init_workqueue(); fsverity_init_sysctl(); fsverity_init_signature(); + fsverity_init_bpf(); return 0; } late_initcall(fsverity_init) diff --git a/fs/verity/measure.c b/fs/verity/measure.c index eec5956141da..a08177eda96e 100644 --- a/fs/verity/measure.c +++ b/fs/verity/measure.c @@ -7,6 +7,8 @@ #include "fsverity_private.h" +#include <linux/bpf.h> +#include <linux/btf.h> #include <linux/uaccess.h> /** @@ -100,3 +102,86 @@ int fsverity_get_digest(struct inode *inode, return hash_alg->digest_size; } EXPORT_SYMBOL_GPL(fsverity_get_digest); + +#ifdef CONFIG_BPF_SYSCALL + +/* bpf kfuncs */ +__diag_push(); +__diag_ignore_all("-Wmissing-prototypes", + "kfuncs which will be used in BPF programs"); + +/** + * bpf_get_fsverity_digest: read fsverity digest of file + * @file: file to get digest from + * @digest_ptr: (out) dynptr for struct fsverity_digest + * + * Read fsverity_digest of *file* into *digest_ptr*. + * + * Return: 0 on success, a negative value on error. + */ +__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, struct bpf_dynptr_kern *digest_ptr) +{ + const struct inode *inode = file_inode(file); + struct fsverity_digest *arg; + const struct fsverity_info *vi; + const struct fsverity_hash_alg *hash_alg; + int out_digest_sz; + + arg = __bpf_dynptr_data_rw(digest_ptr, __bpf_dynptr_size(digest_ptr)); + if (!arg) + return -EINVAL; + + if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg))) + return -EINVAL; + + if (__bpf_dynptr_size(digest_ptr) < sizeof(struct fsverity_digest)) + return -EINVAL; + + vi = fsverity_get_info(inode); + if (!vi) + return -ENODATA; /* not a verity file */ + + hash_alg = vi->tree_params.hash_alg; + + arg->digest_algorithm = hash_alg - fsverity_hash_algs; + arg->digest_size = hash_alg->digest_size; + + out_digest_sz = __bpf_dynptr_size(digest_ptr) - sizeof(struct fsverity_digest); + + /* copy digest */ + memcpy(arg->digest, vi->file_digest, min_t(int, hash_alg->digest_size, out_digest_sz)); + + /* fill the extra buffer with zeros */ + if (out_digest_sz > hash_alg->digest_size) + memset(arg->digest + arg->digest_size, 0, out_digest_sz - hash_alg->digest_size); + + return 0; +} + +__diag_pop(); + +BTF_SET8_START(fsverity_set_ids) +BTF_ID_FLAGS(func, bpf_get_fsverity_digest, KF_TRUSTED_ARGS) +BTF_SET8_END(fsverity_set_ids) + +static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id) +{ + if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id)) + return 0; + + /* Only allow to attach from LSM hooks, to avoid recursion */ + return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0; +} + +static const struct btf_kfunc_id_set bpf_fsverity_set = { + .owner = THIS_MODULE, + .set = &fsverity_set_ids, + .filter = bpf_get_fsverity_digest_filter, +}; + +void __init fsverity_init_bpf(void) +{ + register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); +} + +#endif /* CONFIG_BPF_SYSCALL */