| Message ID | 20231024063056.1008702-6-song@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: File verification with LSM and fsverity | expand |
On Mon, Oct 23, 2023 at 11:30:52PM -0700, Song Liu 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> > --- > 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..f7124f89ab6f 100644 > --- a/fs/verity/fsverity_private.h > +++ b/fs/verity/fsverity_private.h > @@ -145,4 +145,14 @@ static inline void fsverity_init_signature(void) > > void __init fsverity_init_workqueue(void); > > +/* measure.c */ > + > +#ifdef CONFIG_BPF_SYSCALL > +int __init fsverity_init_bpf(void); > +#else > +static inline int fsverity_init_bpf(void) > +{ > +} > +#endif This does not compile when !CONFIG_BPF_SYSCALL. fsverity_init_bpf() probably shouldn't have a return value, given that this code cannot be compiled as a loadable module. You can either panic on error, or ignore the error. I don't think there are any other options. Also, please keep the sections of this file in alphabetical order. The measure.c section should go between init.c and open.c sections. > diff --git a/fs/verity/measure.c b/fs/verity/measure.c > index eec5956141da..4b0617ea0499 100644 > --- a/fs/verity/measure.c > +++ b/fs/verity/measure.c > @@ -8,6 +8,8 @@ > #include "fsverity_private.h" > > #include <linux/uaccess.h> > +#include <linux/bpf.h> > +#include <linux/btf.h> Keep includes in alphabetical order, please. - Eric
> On Oct 24, 2023, at 4:03 PM, Eric Biggers <ebiggers@kernel.org> wrote: > > On Mon, Oct 23, 2023 at 11:30:52PM -0700, Song Liu 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> >> --- >> 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..f7124f89ab6f 100644 >> --- a/fs/verity/fsverity_private.h >> +++ b/fs/verity/fsverity_private.h >> @@ -145,4 +145,14 @@ static inline void fsverity_init_signature(void) >> >> void __init fsverity_init_workqueue(void); >> >> +/* measure.c */ >> + >> +#ifdef CONFIG_BPF_SYSCALL >> +int __init fsverity_init_bpf(void); >> +#else >> +static inline int fsverity_init_bpf(void) >> +{ >> +} >> +#endif > > This does not compile when !CONFIG_BPF_SYSCALL. > > fsverity_init_bpf() probably shouldn't have a return value, given that this code > cannot be compiled as a loadable module. You can either panic on error, or > ignore the error. I don't think there are any other options. Got it. Updated fsverity_init_bpf to return void. > > Also, please keep the sections of this file in alphabetical order. The > measure.c section should go between init.c and open.c sections. > > >> diff --git a/fs/verity/measure.c b/fs/verity/measure.c >> index eec5956141da..4b0617ea0499 100644 >> --- a/fs/verity/measure.c >> +++ b/fs/verity/measure.c >> @@ -8,6 +8,8 @@ >> #include "fsverity_private.h" >> >> #include <linux/uaccess.h> >> +#include <linux/bpf.h> >> +#include <linux/btf.h> > > Keep includes in alphabetical order, please. Fixed in the next version. Thanks, Song
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index d071a6e32581..f7124f89ab6f 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -145,4 +145,14 @@ static inline void fsverity_init_signature(void) void __init fsverity_init_workqueue(void); +/* measure.c */ + +#ifdef CONFIG_BPF_SYSCALL +int __init fsverity_init_bpf(void); +#else +static inline int fsverity_init_bpf(void) +{ +} +#endif + #endif /* _FSVERITY_PRIVATE_H */ 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..4b0617ea0499 100644 --- a/fs/verity/measure.c +++ b/fs/verity/measure.c @@ -8,6 +8,8 @@ #include "fsverity_private.h" #include <linux/uaccess.h> +#include <linux/bpf.h> +#include <linux/btf.h> /** * fsverity_ioctl_measure() - get a verity file's digest @@ -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_slice_rdwr(digest_ptr, 0, NULL, 0); + if (IS_ERR_OR_NULL(arg)) + return PTR_ERR(arg); + + 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) +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, +}; + +int __init fsverity_init_bpf(void) +{ + return register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set); +} + +#endif /* CONFIG_BPF_SYSCALL */
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> --- fs/verity/fsverity_private.h | 10 +++++ fs/verity/init.c | 1 + fs/verity/measure.c | 85 ++++++++++++++++++++++++++++++++++++ 3 files changed, 96 insertions(+)