From: KP Singh <[email protected]>
Adds a callback which is called when a new program is attached
to a hook. The callback registered by the process_exection hook
checks if a program that has calls to a helper that requires pages to
be pinned (eg. krsi_get_env_var).
Signed-off-by: KP Singh <[email protected]>
---
include/linux/krsi.h | 1 +
security/krsi/include/hooks.h | 5 ++-
security/krsi/include/krsi_init.h | 7 ++++
security/krsi/krsi.c | 62 ++++++++++++++++++++++++++++---
security/krsi/ops.c | 10 ++++-
5 files changed, 77 insertions(+), 8 deletions(-)
diff --git a/include/linux/krsi.h b/include/linux/krsi.h
index c7d1790d0c1f..e443d0309764 100644
--- a/include/linux/krsi.h
+++ b/include/linux/krsi.h
@@ -7,6 +7,7 @@
#ifdef CONFIG_SECURITY_KRSI
int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+extern const struct bpf_func_proto krsi_get_env_var_proto;
#else
static inline int krsi_prog_attach(const union bpf_attr *attr,
struct bpf_prog *prog)
diff --git a/security/krsi/include/hooks.h b/security/krsi/include/hooks.h
index e070c452b5de..38293125ff99 100644
--- a/security/krsi/include/hooks.h
+++ b/security/krsi/include/hooks.h
@@ -8,7 +8,7 @@
*
* Format:
*
- * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN)
+ * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN, CALLBACK)
*
* KRSI adds one layer of indirection between the name of the hook and the name
* it exposes to the userspace in Security FS to prevent the userspace from
@@ -18,4 +18,5 @@
KRSI_HOOK_INIT(PROCESS_EXECUTION,
process_execution,
bprm_check_security,
- krsi_process_execution)
+ krsi_process_execution,
+ krsi_process_execution_cb)
diff --git a/security/krsi/include/krsi_init.h b/security/krsi/include/krsi_init.h
index 6152847c3b08..99801d5b273a 100644
--- a/security/krsi/include/krsi_init.h
+++ b/security/krsi/include/krsi_init.h
@@ -31,6 +31,8 @@ struct krsi_ctx {
};
};
+typedef int (*krsi_prog_attach_t) (struct bpf_prog_array *);
+
/*
* The LSM creates one file per hook.
*
@@ -61,6 +63,11 @@ struct krsi_hook {
* The eBPF programs that are attached to this hook.
*/
struct bpf_prog_array __rcu *progs;
+ /*
+ * The attach callback is called before a new program is attached
+ * to the hook and is passed the updated bpf_prog_array as an argument.
+ */
+ krsi_prog_attach_t attach_callback;
};
extern struct krsi_hook krsi_hooks_list[];
diff --git a/security/krsi/krsi.c b/security/krsi/krsi.c
index 00a7150c1b22..a4443d7aa150 100644
--- a/security/krsi/krsi.c
+++ b/security/krsi/krsi.c
@@ -5,15 +5,65 @@
#include <linux/bpf.h>
#include <linux/binfmts.h>
#include <linux/highmem.h>
+#include <linux/krsi.h>
#include <linux/mm.h>
#include "krsi_init.h"
+/*
+ * need_arg_pages is only updated in bprm_check_security_cb
+ * when a mutex on krsi_hook for bprm_check_security is already
+ * held. need_arg_pages avoids pinning pages when no program
+ * that needs them is attached to the hook.
+ */
+static bool need_arg_pages;
+
+/*
+ * Checks if the instruction is a BPF_CALL to an eBPF helper located
+ * at the given address.
+ */
+static inline bool bpf_is_call_to_func(struct bpf_insn *insn,
+ void *func_addr)
+{
+ u8 opcode = BPF_OP(insn->code);
+
+ if (opcode != BPF_CALL)
+ return false;
+
+ if (insn->src_reg == BPF_PSEUDO_CALL)
+ return false;
+
+ /*
+ * The BPF verifier updates the value of insn->imm from the
+ * enum bpf_func_id to the offset of the address of helper
+ * from the __bpf_call_base.
+ */
+ return __bpf_call_base + insn->imm == func_addr;
+}
+
+static int krsi_process_execution_cb(struct bpf_prog_array *array)
+{
+ struct bpf_prog_array_item *item = array->items;
+ struct bpf_prog *p;
+ const struct bpf_func_proto *proto = &krsi_get_env_var_proto;
+ int i;
+
+ while ((p = READ_ONCE(item->prog))) {
+ for (i = 0; i < p->len; i++) {
+ if (bpf_is_call_to_func(&p->insnsi[i], proto->func))
+ need_arg_pages = true;
+ }
+ item++;
+ }
+ return 0;
+}
+
struct krsi_hook krsi_hooks_list[] = {
- #define KRSI_HOOK_INIT(TYPE, NAME, H, I) \
+ #define KRSI_HOOK_INIT(TYPE, NAME, H, I, CB) \
[TYPE] = { \
.h_type = TYPE, \
.name = #NAME, \
+ .attach_callback = CB, \
},
#include "hooks.h"
#undef KRSI_HOOK_INIT
@@ -75,9 +125,11 @@ static int krsi_process_execution(struct linux_binprm *bprm)
.bprm = bprm,
};
- ret = pin_arg_pages(&ctx.bprm_ctx);
- if (ret < 0)
- goto out_arg_pages;
+ if (READ_ONCE(need_arg_pages)) {
+ ret = pin_arg_pages(&ctx.bprm_ctx);
+ if (ret < 0)
+ goto out_arg_pages;
+ }
ret = krsi_run_progs(PROCESS_EXECUTION, &ctx);
kfree(ctx.bprm_ctx.arg_pages);
@@ -87,7 +139,7 @@ static int krsi_process_execution(struct linux_binprm *bprm)
}
static struct security_hook_list krsi_hooks[] __lsm_ro_after_init = {
- #define KRSI_HOOK_INIT(T, N, HOOK, IMPL) LSM_HOOK_INIT(HOOK, IMPL),
+ #define KRSI_HOOK_INIT(T, N, HOOK, IMPL, CB) LSM_HOOK_INIT(HOOK, IMPL),
#include "hooks.h"
#undef KRSI_HOOK_INIT
};
diff --git a/security/krsi/ops.c b/security/krsi/ops.c
index 1db94dfaac15..2de682371eff 100644
--- a/security/krsi/ops.c
+++ b/security/krsi/ops.c
@@ -139,6 +139,14 @@ int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
goto unlock;
}
+ if (h->attach_callback) {
+ ret = h->attach_callback(new_array);
+ if (ret < 0) {
+ bpf_prog_array_free(new_array);
+ goto unlock;
+ }
+ }
+
rcu_assign_pointer(h->progs, new_array);
bpf_prog_array_free(old_array);
@@ -278,7 +286,7 @@ BPF_CALL_5(krsi_get_env_var, struct krsi_ctx *, ctx, char *, name, u32, n_size,
return get_env_var(ctx, name, dest, n_size, size);
}
-static const struct bpf_func_proto krsi_get_env_var_proto = {
+const struct bpf_func_proto krsi_get_env_var_proto = {
.func = krsi_get_env_var,
.gpl_only = true,
.ret_type = RET_INTEGER,
--
2.20.1
On 15-Sep 00:33, Yonghong Song wrote:
>
>
> On 9/10/19 12:55 PM, KP Singh wrote:
> > From: KP Singh <[email protected]>
> >
> > Adds a callback which is called when a new program is attached
> > to a hook. The callback registered by the process_exection hook
> > checks if a program that has calls to a helper that requires pages to
> > be pinned (eg. krsi_get_env_var).
> >
> > Signed-off-by: KP Singh <[email protected]>
> > ---
> > include/linux/krsi.h | 1 +
> > security/krsi/include/hooks.h | 5 ++-
> > security/krsi/include/krsi_init.h | 7 ++++
> > security/krsi/krsi.c | 62 ++++++++++++++++++++++++++++---
> > security/krsi/ops.c | 10 ++++-
> > 5 files changed, 77 insertions(+), 8 deletions(-)
> >
> > diff --git a/include/linux/krsi.h b/include/linux/krsi.h
> > index c7d1790d0c1f..e443d0309764 100644
> > --- a/include/linux/krsi.h
> > +++ b/include/linux/krsi.h
> > @@ -7,6 +7,7 @@
> >
> > #ifdef CONFIG_SECURITY_KRSI
> > int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> > +extern const struct bpf_func_proto krsi_get_env_var_proto;
> > #else
> > static inline int krsi_prog_attach(const union bpf_attr *attr,
> > struct bpf_prog *prog)
> > diff --git a/security/krsi/include/hooks.h b/security/krsi/include/hooks.h
> > index e070c452b5de..38293125ff99 100644
> > --- a/security/krsi/include/hooks.h
> > +++ b/security/krsi/include/hooks.h
> > @@ -8,7 +8,7 @@
> > *
> > * Format:
> > *
> > - * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN)
> > + * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN, CALLBACK)
> > *
> > * KRSI adds one layer of indirection between the name of the hook and the name
> > * it exposes to the userspace in Security FS to prevent the userspace from
> > @@ -18,4 +18,5 @@
> > KRSI_HOOK_INIT(PROCESS_EXECUTION,
> > process_execution,
> > bprm_check_security,
> > - krsi_process_execution)
> > + krsi_process_execution,
> > + krsi_process_execution_cb)
> > diff --git a/security/krsi/include/krsi_init.h b/security/krsi/include/krsi_init.h
> > index 6152847c3b08..99801d5b273a 100644
> > --- a/security/krsi/include/krsi_init.h
> > +++ b/security/krsi/include/krsi_init.h
> > @@ -31,6 +31,8 @@ struct krsi_ctx {
> > };
> > };
> >
> > +typedef int (*krsi_prog_attach_t) (struct bpf_prog_array *);
> > +
> > /*
> > * The LSM creates one file per hook.
> > *
> > @@ -61,6 +63,11 @@ struct krsi_hook {
> > * The eBPF programs that are attached to this hook.
> > */
> > struct bpf_prog_array __rcu *progs;
> > + /*
> > + * The attach callback is called before a new program is attached
> > + * to the hook and is passed the updated bpf_prog_array as an argument.
> > + */
> > + krsi_prog_attach_t attach_callback;
> > };
> >
> > extern struct krsi_hook krsi_hooks_list[];
> > diff --git a/security/krsi/krsi.c b/security/krsi/krsi.c
> > index 00a7150c1b22..a4443d7aa150 100644
> > --- a/security/krsi/krsi.c
> > +++ b/security/krsi/krsi.c
> > @@ -5,15 +5,65 @@
> > #include <linux/bpf.h>
> > #include <linux/binfmts.h>
> > #include <linux/highmem.h>
> > +#include <linux/krsi.h>
> > #include <linux/mm.h>
> >
> > #include "krsi_init.h"
> >
> > +/*
> > + * need_arg_pages is only updated in bprm_check_security_cb
> > + * when a mutex on krsi_hook for bprm_check_security is already
> > + * held. need_arg_pages avoids pinning pages when no program
> > + * that needs them is attached to the hook.
> > + */
> > +static bool need_arg_pages;
> > +
> > +/*
> > + * Checks if the instruction is a BPF_CALL to an eBPF helper located
> > + * at the given address.
> > + */
> > +static inline bool bpf_is_call_to_func(struct bpf_insn *insn,
> > + void *func_addr)
> > +{
> > + u8 opcode = BPF_OP(insn->code);
> > +
> > + if (opcode != BPF_CALL)
> > + return false;
> > +
> > + if (insn->src_reg == BPF_PSEUDO_CALL)
> > + return false;
> > +
> > + /*
> > + * The BPF verifier updates the value of insn->imm from the
> > + * enum bpf_func_id to the offset of the address of helper
> > + * from the __bpf_call_base.
> > + */
> > + return __bpf_call_base + insn->imm == func_addr;
>
> In how many cases, krsi program does not have krsi_get_env_var() helper?
It depends, if the user does not choose to use log environment
variables or use the the value as a part of their MAC policy, the
pinning of the pages is not needed.
Also, the pinning is needed since eBPF helpers cannot run a non-atomic
context. It would not be needed if "sleepable eBPF" becomes a thing.
- KP
>
> > +}
> > +
> > +static int krsi_process_execution_cb(struct bpf_prog_array *array)
> > +{
> > + struct bpf_prog_array_item *item = array->items;
> > + struct bpf_prog *p;
> > + const struct bpf_func_proto *proto = &krsi_get_env_var_proto;
> > + int i;
> > +
> > + while ((p = READ_ONCE(item->prog))) {
> > + for (i = 0; i < p->len; i++) {
> > + if (bpf_is_call_to_func(&p->insnsi[i], proto->func))
> > + need_arg_pages = true;
> > + }
> > + item++;
> > + }
> > + return 0;
> > +}
> > +
> > struct krsi_hook krsi_hooks_list[] = {
> > - #define KRSI_HOOK_INIT(TYPE, NAME, H, I) \
> > + #define KRSI_HOOK_INIT(TYPE, NAME, H, I, CB) \
> > [TYPE] = { \
> > .h_type = TYPE, \
> > .name = #NAME, \
> > + .attach_callback = CB, \
> > },
> > #include "hooks.h"
> > #undef KRSI_HOOK_INIT
> > @@ -75,9 +125,11 @@ static int krsi_process_execution(struct linux_binprm *bprm)
> > .bprm = bprm,
> > };
> >
> > - ret = pin_arg_pages(&ctx.bprm_ctx);
> > - if (ret < 0)
> > - goto out_arg_pages;
> > + if (READ_ONCE(need_arg_pages)) {
> > + ret = pin_arg_pages(&ctx.bprm_ctx);
> > + if (ret < 0)
> > + goto out_arg_pages;
> > + }
> >
> > ret = krsi_run_progs(PROCESS_EXECUTION, &ctx);
> > kfree(ctx.bprm_ctx.arg_pages);
> > @@ -87,7 +139,7 @@ static int krsi_process_execution(struct linux_binprm *bprm)
> > }
> >
> > static struct security_hook_list krsi_hooks[] __lsm_ro_after_init = {
> > - #define KRSI_HOOK_INIT(T, N, HOOK, IMPL) LSM_HOOK_INIT(HOOK, IMPL),
> > + #define KRSI_HOOK_INIT(T, N, HOOK, IMPL, CB) LSM_HOOK_INIT(HOOK, IMPL),
> > #include "hooks.h"
> > #undef KRSI_HOOK_INIT
> > };
> > diff --git a/security/krsi/ops.c b/security/krsi/ops.c
> > index 1db94dfaac15..2de682371eff 100644
> > --- a/security/krsi/ops.c
> > +++ b/security/krsi/ops.c
> > @@ -139,6 +139,14 @@ int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> > goto unlock;
> > }
> >
> > + if (h->attach_callback) {
> > + ret = h->attach_callback(new_array);
> > + if (ret < 0) {
> > + bpf_prog_array_free(new_array);
> > + goto unlock;
> > + }
> > + }
> > +
> > rcu_assign_pointer(h->progs, new_array);
> > bpf_prog_array_free(old_array);
> >
> > @@ -278,7 +286,7 @@ BPF_CALL_5(krsi_get_env_var, struct krsi_ctx *, ctx, char *, name, u32, n_size,
> > return get_env_var(ctx, name, dest, n_size, size);
> > }
> >
> > -static const struct bpf_func_proto krsi_get_env_var_proto = {
> > +const struct bpf_func_proto krsi_get_env_var_proto = {
> > .func = krsi_get_env_var,
> > .gpl_only = true,
> > .ret_type = RET_INTEGER,
> >
On 9/10/19 12:55 PM, KP Singh wrote:
> From: KP Singh <[email protected]>
>
> Adds a callback which is called when a new program is attached
> to a hook. The callback registered by the process_exection hook
> checks if a program that has calls to a helper that requires pages to
> be pinned (eg. krsi_get_env_var).
>
> Signed-off-by: KP Singh <[email protected]>
> ---
> include/linux/krsi.h | 1 +
> security/krsi/include/hooks.h | 5 ++-
> security/krsi/include/krsi_init.h | 7 ++++
> security/krsi/krsi.c | 62 ++++++++++++++++++++++++++++---
> security/krsi/ops.c | 10 ++++-
> 5 files changed, 77 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/krsi.h b/include/linux/krsi.h
> index c7d1790d0c1f..e443d0309764 100644
> --- a/include/linux/krsi.h
> +++ b/include/linux/krsi.h
> @@ -7,6 +7,7 @@
>
> #ifdef CONFIG_SECURITY_KRSI
> int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog);
> +extern const struct bpf_func_proto krsi_get_env_var_proto;
> #else
> static inline int krsi_prog_attach(const union bpf_attr *attr,
> struct bpf_prog *prog)
> diff --git a/security/krsi/include/hooks.h b/security/krsi/include/hooks.h
> index e070c452b5de..38293125ff99 100644
> --- a/security/krsi/include/hooks.h
> +++ b/security/krsi/include/hooks.h
> @@ -8,7 +8,7 @@
> *
> * Format:
> *
> - * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN)
> + * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN, CALLBACK)
> *
> * KRSI adds one layer of indirection between the name of the hook and the name
> * it exposes to the userspace in Security FS to prevent the userspace from
> @@ -18,4 +18,5 @@
> KRSI_HOOK_INIT(PROCESS_EXECUTION,
> process_execution,
> bprm_check_security,
> - krsi_process_execution)
> + krsi_process_execution,
> + krsi_process_execution_cb)
> diff --git a/security/krsi/include/krsi_init.h b/security/krsi/include/krsi_init.h
> index 6152847c3b08..99801d5b273a 100644
> --- a/security/krsi/include/krsi_init.h
> +++ b/security/krsi/include/krsi_init.h
> @@ -31,6 +31,8 @@ struct krsi_ctx {
> };
> };
>
> +typedef int (*krsi_prog_attach_t) (struct bpf_prog_array *);
> +
> /*
> * The LSM creates one file per hook.
> *
> @@ -61,6 +63,11 @@ struct krsi_hook {
> * The eBPF programs that are attached to this hook.
> */
> struct bpf_prog_array __rcu *progs;
> + /*
> + * The attach callback is called before a new program is attached
> + * to the hook and is passed the updated bpf_prog_array as an argument.
> + */
> + krsi_prog_attach_t attach_callback;
> };
>
> extern struct krsi_hook krsi_hooks_list[];
> diff --git a/security/krsi/krsi.c b/security/krsi/krsi.c
> index 00a7150c1b22..a4443d7aa150 100644
> --- a/security/krsi/krsi.c
> +++ b/security/krsi/krsi.c
> @@ -5,15 +5,65 @@
> #include <linux/bpf.h>
> #include <linux/binfmts.h>
> #include <linux/highmem.h>
> +#include <linux/krsi.h>
> #include <linux/mm.h>
>
> #include "krsi_init.h"
>
> +/*
> + * need_arg_pages is only updated in bprm_check_security_cb
> + * when a mutex on krsi_hook for bprm_check_security is already
> + * held. need_arg_pages avoids pinning pages when no program
> + * that needs them is attached to the hook.
> + */
> +static bool need_arg_pages;
> +
> +/*
> + * Checks if the instruction is a BPF_CALL to an eBPF helper located
> + * at the given address.
> + */
> +static inline bool bpf_is_call_to_func(struct bpf_insn *insn,
> + void *func_addr)
> +{
> + u8 opcode = BPF_OP(insn->code);
> +
> + if (opcode != BPF_CALL)
> + return false;
> +
> + if (insn->src_reg == BPF_PSEUDO_CALL)
> + return false;
> +
> + /*
> + * The BPF verifier updates the value of insn->imm from the
> + * enum bpf_func_id to the offset of the address of helper
> + * from the __bpf_call_base.
> + */
> + return __bpf_call_base + insn->imm == func_addr;
In how many cases, krsi program does not have krsi_get_env_var() helper?
> +}
> +
> +static int krsi_process_execution_cb(struct bpf_prog_array *array)
> +{
> + struct bpf_prog_array_item *item = array->items;
> + struct bpf_prog *p;
> + const struct bpf_func_proto *proto = &krsi_get_env_var_proto;
> + int i;
> +
> + while ((p = READ_ONCE(item->prog))) {
> + for (i = 0; i < p->len; i++) {
> + if (bpf_is_call_to_func(&p->insnsi[i], proto->func))
> + need_arg_pages = true;
> + }
> + item++;
> + }
> + return 0;
> +}
> +
> struct krsi_hook krsi_hooks_list[] = {
> - #define KRSI_HOOK_INIT(TYPE, NAME, H, I) \
> + #define KRSI_HOOK_INIT(TYPE, NAME, H, I, CB) \
> [TYPE] = { \
> .h_type = TYPE, \
> .name = #NAME, \
> + .attach_callback = CB, \
> },
> #include "hooks.h"
> #undef KRSI_HOOK_INIT
> @@ -75,9 +125,11 @@ static int krsi_process_execution(struct linux_binprm *bprm)
> .bprm = bprm,
> };
>
> - ret = pin_arg_pages(&ctx.bprm_ctx);
> - if (ret < 0)
> - goto out_arg_pages;
> + if (READ_ONCE(need_arg_pages)) {
> + ret = pin_arg_pages(&ctx.bprm_ctx);
> + if (ret < 0)
> + goto out_arg_pages;
> + }
>
> ret = krsi_run_progs(PROCESS_EXECUTION, &ctx);
> kfree(ctx.bprm_ctx.arg_pages);
> @@ -87,7 +139,7 @@ static int krsi_process_execution(struct linux_binprm *bprm)
> }
>
> static struct security_hook_list krsi_hooks[] __lsm_ro_after_init = {
> - #define KRSI_HOOK_INIT(T, N, HOOK, IMPL) LSM_HOOK_INIT(HOOK, IMPL),
> + #define KRSI_HOOK_INIT(T, N, HOOK, IMPL, CB) LSM_HOOK_INIT(HOOK, IMPL),
> #include "hooks.h"
> #undef KRSI_HOOK_INIT
> };
> diff --git a/security/krsi/ops.c b/security/krsi/ops.c
> index 1db94dfaac15..2de682371eff 100644
> --- a/security/krsi/ops.c
> +++ b/security/krsi/ops.c
> @@ -139,6 +139,14 @@ int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> goto unlock;
> }
>
> + if (h->attach_callback) {
> + ret = h->attach_callback(new_array);
> + if (ret < 0) {
> + bpf_prog_array_free(new_array);
> + goto unlock;
> + }
> + }
> +
> rcu_assign_pointer(h->progs, new_array);
> bpf_prog_array_free(old_array);
>
> @@ -278,7 +286,7 @@ BPF_CALL_5(krsi_get_env_var, struct krsi_ctx *, ctx, char *, name, u32, n_size,
> return get_env_var(ctx, name, dest, n_size, size);
> }
>
> -static const struct bpf_func_proto krsi_get_env_var_proto = {
> +const struct bpf_func_proto krsi_get_env_var_proto = {
> .func = krsi_get_env_var,
> .gpl_only = true,
> .ret_type = RET_INTEGER,
>
On 9/15/19 2:40 AM, KP Singh wrote:
> On 15-Sep 00:33, Yonghong Song wrote:
>>
>>
>> On 9/10/19 12:55 PM, KP Singh wrote:
>>> From: KP Singh <[email protected]>
>>>
>>> Adds a callback which is called when a new program is attached
>>> to a hook. The callback registered by the process_exection hook
>>> checks if a program that has calls to a helper that requires pages to
>>> be pinned (eg. krsi_get_env_var).
>>>
>>> Signed-off-by: KP Singh <[email protected]>
>>> ---
>>> include/linux/krsi.h | 1 +
>>> security/krsi/include/hooks.h | 5 ++-
>>> security/krsi/include/krsi_init.h | 7 ++++
>>> security/krsi/krsi.c | 62 ++++++++++++++++++++++++++++---
>>> security/krsi/ops.c | 10 ++++-
>>> 5 files changed, 77 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/include/linux/krsi.h b/include/linux/krsi.h
>>> index c7d1790d0c1f..e443d0309764 100644
>>> --- a/include/linux/krsi.h
>>> +++ b/include/linux/krsi.h
>>> @@ -7,6 +7,7 @@
>>>
>>> #ifdef CONFIG_SECURITY_KRSI
>>> int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog);
>>> +extern const struct bpf_func_proto krsi_get_env_var_proto;
>>> #else
>>> static inline int krsi_prog_attach(const union bpf_attr *attr,
>>> struct bpf_prog *prog)
>>> diff --git a/security/krsi/include/hooks.h b/security/krsi/include/hooks.h
>>> index e070c452b5de..38293125ff99 100644
>>> --- a/security/krsi/include/hooks.h
>>> +++ b/security/krsi/include/hooks.h
>>> @@ -8,7 +8,7 @@
>>> *
>>> * Format:
>>> *
>>> - * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN)
>>> + * KRSI_HOOK_INIT(TYPE, NAME, LSM_HOOK, KRSI_HOOK_FN, CALLBACK)
>>> *
>>> * KRSI adds one layer of indirection between the name of the hook and the name
>>> * it exposes to the userspace in Security FS to prevent the userspace from
>>> @@ -18,4 +18,5 @@
>>> KRSI_HOOK_INIT(PROCESS_EXECUTION,
>>> process_execution,
>>> bprm_check_security,
>>> - krsi_process_execution)
>>> + krsi_process_execution,
>>> + krsi_process_execution_cb)
>>> diff --git a/security/krsi/include/krsi_init.h b/security/krsi/include/krsi_init.h
>>> index 6152847c3b08..99801d5b273a 100644
>>> --- a/security/krsi/include/krsi_init.h
>>> +++ b/security/krsi/include/krsi_init.h
>>> @@ -31,6 +31,8 @@ struct krsi_ctx {
>>> };
>>> };
>>>
>>> +typedef int (*krsi_prog_attach_t) (struct bpf_prog_array *);
>>> +
>>> /*
>>> * The LSM creates one file per hook.
>>> *
>>> @@ -61,6 +63,11 @@ struct krsi_hook {
>>> * The eBPF programs that are attached to this hook.
>>> */
>>> struct bpf_prog_array __rcu *progs;
>>> + /*
>>> + * The attach callback is called before a new program is attached
>>> + * to the hook and is passed the updated bpf_prog_array as an argument.
>>> + */
>>> + krsi_prog_attach_t attach_callback;
>>> };
>>>
>>> extern struct krsi_hook krsi_hooks_list[];
>>> diff --git a/security/krsi/krsi.c b/security/krsi/krsi.c
>>> index 00a7150c1b22..a4443d7aa150 100644
>>> --- a/security/krsi/krsi.c
>>> +++ b/security/krsi/krsi.c
>>> @@ -5,15 +5,65 @@
>>> #include <linux/bpf.h>
>>> #include <linux/binfmts.h>
>>> #include <linux/highmem.h>
>>> +#include <linux/krsi.h>
>>> #include <linux/mm.h>
>>>
>>> #include "krsi_init.h"
>>>
>>> +/*
>>> + * need_arg_pages is only updated in bprm_check_security_cb
>>> + * when a mutex on krsi_hook for bprm_check_security is already
>>> + * held. need_arg_pages avoids pinning pages when no program
>>> + * that needs them is attached to the hook.
>>> + */
>>> +static bool need_arg_pages;
>>> +
>>> +/*
>>> + * Checks if the instruction is a BPF_CALL to an eBPF helper located
>>> + * at the given address.
>>> + */
>>> +static inline bool bpf_is_call_to_func(struct bpf_insn *insn,
>>> + void *func_addr)
>>> +{
>>> + u8 opcode = BPF_OP(insn->code);
>>> +
>>> + if (opcode != BPF_CALL)
>>> + return false;
>>> +
>>> + if (insn->src_reg == BPF_PSEUDO_CALL)
>>> + return false;
>>> +
>>> + /*
>>> + * The BPF verifier updates the value of insn->imm from the
>>> + * enum bpf_func_id to the offset of the address of helper
>>> + * from the __bpf_call_base.
>>> + */
>>> + return __bpf_call_base + insn->imm == func_addr;
>>
>> In how many cases, krsi program does not have krsi_get_env_var() helper?
>
> It depends, if the user does not choose to use log environment
> variables or use the the value as a part of their MAC policy, the
> pinning of the pages is not needed.
Thanks. I just want to know whether we want to optimize such cases.
I am not a security expert, so I am okay with whatever decision you
made.
>
> Also, the pinning is needed since eBPF helpers cannot run a non-atomic
> context. It would not be needed if "sleepable eBPF" becomes a thing.
Indeed. 'sleepable BPF' might be also a good thing for realtime linux.
Some works need to address bpf area spin lock, per cpu variables, etc.
before that can happen.
>
> - KP
>
>>
>>> +}
>>> +
>>> +static int krsi_process_execution_cb(struct bpf_prog_array *array)
>>> +{
>>> + struct bpf_prog_array_item *item = array->items;
>>> + struct bpf_prog *p;
>>> + const struct bpf_func_proto *proto = &krsi_get_env_var_proto;
>>> + int i;
>>> +
>>> + while ((p = READ_ONCE(item->prog))) {
>>> + for (i = 0; i < p->len; i++) {
>>> + if (bpf_is_call_to_func(&p->insnsi[i], proto->func))
>>> + need_arg_pages = true;
>>> + }
>>> + item++;
>>> + }
>>> + return 0;
>>> +}
>>> +
>>> struct krsi_hook krsi_hooks_list[] = {
>>> - #define KRSI_HOOK_INIT(TYPE, NAME, H, I) \
>>> + #define KRSI_HOOK_INIT(TYPE, NAME, H, I, CB) \
>>> [TYPE] = { \
>>> .h_type = TYPE, \
>>> .name = #NAME, \
>>> + .attach_callback = CB, \
>>> },
>>> #include "hooks.h"
>>> #undef KRSI_HOOK_INIT
>>> @@ -75,9 +125,11 @@ static int krsi_process_execution(struct linux_binprm *bprm)
>>> .bprm = bprm,
>>> };
>>>
>>> - ret = pin_arg_pages(&ctx.bprm_ctx);
>>> - if (ret < 0)
>>> - goto out_arg_pages;
>>> + if (READ_ONCE(need_arg_pages)) {
>>> + ret = pin_arg_pages(&ctx.bprm_ctx);
>>> + if (ret < 0)
>>> + goto out_arg_pages;
>>> + }
>>>
>>> ret = krsi_run_progs(PROCESS_EXECUTION, &ctx);
>>> kfree(ctx.bprm_ctx.arg_pages);
>>> @@ -87,7 +139,7 @@ static int krsi_process_execution(struct linux_binprm *bprm)
>>> }
>>>
>>> static struct security_hook_list krsi_hooks[] __lsm_ro_after_init = {
>>> - #define KRSI_HOOK_INIT(T, N, HOOK, IMPL) LSM_HOOK_INIT(HOOK, IMPL),
>>> + #define KRSI_HOOK_INIT(T, N, HOOK, IMPL, CB) LSM_HOOK_INIT(HOOK, IMPL),
>>> #include "hooks.h"
>>> #undef KRSI_HOOK_INIT
>>> };
>>> diff --git a/security/krsi/ops.c b/security/krsi/ops.c
>>> index 1db94dfaac15..2de682371eff 100644
>>> --- a/security/krsi/ops.c
>>> +++ b/security/krsi/ops.c
>>> @@ -139,6 +139,14 @@ int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
>>> goto unlock;
>>> }
>>>
>>> + if (h->attach_callback) {
>>> + ret = h->attach_callback(new_array);
>>> + if (ret < 0) {
>>> + bpf_prog_array_free(new_array);
>>> + goto unlock;
>>> + }
>>> + }
>>> +
>>> rcu_assign_pointer(h->progs, new_array);
>>> bpf_prog_array_free(old_array);
>>>
>>> @@ -278,7 +286,7 @@ BPF_CALL_5(krsi_get_env_var, struct krsi_ctx *, ctx, char *, name, u32, n_size,
>>> return get_env_var(ctx, name, dest, n_size, size);
>>> }
>>>
>>> -static const struct bpf_func_proto krsi_get_env_var_proto = {
>>> +const struct bpf_func_proto krsi_get_env_var_proto = {
>>> .func = krsi_get_env_var,
>>> .gpl_only = true,
>>> .ret_type = RET_INTEGER,
>>>