Re: [PATCH v12 02/10] btf: Handle dynamic pointer parameter in kfuncs

On Thu, Aug 18, 2022 at 05:29:21PM +0200, roberto.sassu@huaweicloud.com wrote:

From: Roberto Sassu roberto.sassu@huawei.com

Allow the bpf_dynptr_kern parameter to be specified in kfuncs. Also, ensure that the dynamic pointer is valid and initialized.

To properly detect whether a parameter is of the desired type, introduce the stringify_struct() macro to compare the returned structure name with the desired name. In addition, protect against structure renames, by halting the build with BUILD_BUG_ON(), so that developers have to revisit the code.

Cc: Joanne Koong joannelkoong@gmail.com Signed-off-by: Roberto Sassu roberto.sassu@huawei.com

---

include/linux/bpf_verifier.h | 3 +++ include/linux/btf.h | 9 +++++++++ kernel/bpf/btf.c | 18 ++++++++++++++++++ kernel/bpf/verifier.c | 4 ++-- 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 2e3bad8640dc..55876fbdbae2 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -560,6 +560,9 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state u32 regno); int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg, u32 regno, u32 mem_size); +bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,

• 	      struct bpf_reg_state *reg,
  

• 	      enum bpf_arg_type arg_type);
  

/* this lives here instead of in bpf.h because it needs to dereference tgt_prog */ static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog, diff --git a/include/linux/btf.h b/include/linux/btf.h index ad93c2d9cc1c..f546d368ac5d 100644 --- a/include/linux/btf.h +++ b/include/linux/btf.h @@ -52,6 +52,15 @@ #define KF_SLEEPABLE (1 << 5) /* kfunc may sleep */ #define KF_DESTRUCTIVE (1 << 6) /* kfunc performs destructive actions */ +/*

• • Return the name of the passed struct, if exists, or halt the build if for
• • example the structure gets renamed. In this way, developers have to revisit
• • the code using that structure name, and update it accordingly.
• */

+#define stringify_struct(x) \

• ({ BUILD_BUG_ON(sizeof(struct x) < 0); \

•   __stringify(x); })
  

struct btf; struct btf_member; struct btf_type; diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index e49b3b6d48ad..26cb548420af 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -6362,15 +6362,20 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, if (is_kfunc) { bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);

• 		bool arg_dynptr = btf_type_is_struct(ref_t) &&
  

• 				  !strcmp(ref_tname,
  

• 					  stringify_struct(bpf_dynptr_kern));
  

/* Permit pointer to mem, but only when argument * type is pointer to scalar, or struct composed * (recursively) of scalars. * When arg_mem_size is true, the pointer can be * void *.

• 		 * Also permit initialized dynamic pointers.
  	 */
  	if (!btf_type_is_scalar(ref_t) &&
  	    !__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
  

• 		    !arg_dynptr &&
  	    (arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
  		bpf_log(log,
  			"arg#%d pointer type %s %s must point to %sscalar, or struct with scalar\n",
  

@@ -6378,6 +6383,19 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, return -EINVAL; }

• 		if (arg_dynptr) {
  

• 			if (!is_dynptr_reg_valid_init(env, reg,
  

• 					ARG_PTR_TO_DYNPTR)) {
  

• 				bpf_log(log,
  

• 					"arg#%d pointer type %s %s must be initialized\n",
  

• 					i, btf_type_str(ref_t),
  

• 					ref_tname);
  

• 				return -EINVAL;
  

• 			}
  

• 			continue;
  

• 		}
  

• 	/* Check for mem, len pair */
  	if (arg_mem_size) {
  		if (check_kfunc_mem_size_reg(env, &regs[regno + 1], regno + 1)) {
  

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 2c1f8069f7b7..aa834e7bb296 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -779,8 +779,8 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_ return true; } -static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,

• 		     enum bpf_arg_type arg_type)
  

+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,

• 	      enum bpf_arg_type arg_type)
  

{ struct bpf_func_state *state = func(env, reg); int spi = get_spi(reg->off); -- 2.25.1

Might be niticking but generally I'd consider splitting exports as commits of their own.

BR, Jarko