[RFC,v1,14/14] krsi: Pin arg pages only when needed
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Message ID 20190910115527.5235-15-kpsingh@chromium.org
State New
Headers show
Series
  • Kernel Runtime Security Instrumentation
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Commit Message

KP Singh Sept. 10, 2019, 11:55 a.m. UTC
From: KP Singh <kpsingh@google.com>

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 <kpsingh@google.com>
---
 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(-)

Comments

Yonghong Song Sept. 15, 2019, 12:33 a.m. UTC | #1
On 9/10/19 12:55 PM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
> 
> 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 <kpsingh@google.com>
> ---
>   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,
>
KP Singh Sept. 15, 2019, 1:40 a.m. UTC | #2
On 15-Sep 00:33, Yonghong Song wrote:
> 
> 
> On 9/10/19 12:55 PM, KP Singh wrote:
> > From: KP Singh <kpsingh@google.com>
> > 
> > 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 <kpsingh@google.com>
> > ---
> >   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,
> >
Yonghong Song Sept. 15, 2019, 7:45 p.m. UTC | #3
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 <kpsingh@google.com>
>>>
>>> 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 <kpsingh@google.com>
>>> ---
>>>    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,
>>>

Patch
diff mbox series

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,