Re: [PATCH v3 bpf-next 3/7] kbuild, btf: Expose vmlinux inline BTF through sysfs

On 03/10/2026 20:56, sashiko-bot@kernel.org wrote:

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] bpf: btf: Unvalidated zero-size allocation triggers WARN_ON_ONCE in vmalloc_user
- [Low] bpf: btf: Linkage fails for sha256 when CONFIG_DEBUG_INFO_BTF_INLINE=m
--

commit de2bb52fc001c93d461a0839a26e550f67f5ecc2
Author: Alan Maguire [off-list ref]

kbuild, btf: Expose vmlinux inline BTF through sysfs

This commit introduces support for embedded and module-delivered vmlinux
inline BTF payloads, making them available via sysfs. It also sets up deferred
binding for a module-provided .BTF.inline section.

quoted

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 134b15a44625e..24abfff1ddc3c 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug

@@ -432,6 +438,19 @@ config DEBUG_INFO_BTF_MODULES
 	help
 	  Generate compact split BTF type information for kernel modules.
 
+config DEBUG_INFO_BTF_INLINE
+	tristate "Provide information about inline sites in BTF"
+	default n
+	depends on DEBUG_INFO_BTF && PAHOLE_HAS_INLINE && SYSFS
+	select DEBUG_INFO_BTF_MODULES if MODULES
+	select CRYPTO_LIB_SHA256

[Severity: Low]
Does this cause a linkage failure when CONFIG_DEBUG_INFO_BTF_INLINE is built
as a module?

Because this is a tristate, selecting CRYPTO_LIB_SHA256 here means it will 
evaluate to 'm' if the inline feature is configured as a module. 

However, the crypto library is called directly from the built-in core kernel
object kernel/bpf/btf.c:

kernel/bpf/btf.c:btf_verify_link() {
    ...
    sha256(data, data_size, actual_digest);
    ...
}

A built-in object cannot resolve a symbol exported by a loadable module,
which will result in an 'undefined reference to sha256' error at build time.

Given that CONFIG_BPF (not tristate) also selects CRYPTO_LIB_SHA256
(making it y) we can simply drop the above select.

 

quoted

+	help
+	  Generate information about inline sites in .BTF.inline sections.

[ ... ]

quoted

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 0630675377aaa..732ba06846675 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c

[ ... ]

quoted

@@ -9015,21 +9016,122 @@ static DEFINE_MUTEX(btf_module_mutex);
+static int btf_module_handle_vmlinux_inline(const struct module *mod)
+{
+	void *data = NULL;
+
+	if (!vmlinux_inline_link || strcmp(mod->name, vmlinux_inline_link->module_name))
+		return -ENOENT;
+
+	data = vmalloc_user(mod->btf_inline_data_size);

[Severity: Medium]
Could this trigger a WARN_ON_ONCE splat in the memory allocation paths?

If a user with CAP_SYS_MODULE loads a module matching
vmlinux_inline_link->module_name, but the module has no .BTF.inline section
(or its size is exactly 0), mod->btf_inline_data_size will be set to 0.

Calling vmalloc_user(0) here happens before the size is validated against 
link->btf_size, which causes a kernel warning in __vmalloc_node_range_noprof.

yeah, we need size checks here prior to vmalloc_user().