Commit a539e2a6 authored by Lorenz Bauer's avatar Lorenz Bauer Committed by Andrii Nakryiko
Browse files

btf: Allow mmap of vmlinux btf 



User space needs access to kernel BTF for many modern features of BPF.
Right now each process needs to read the BTF blob either in pieces or
as a whole. Allow mmaping the sysfs file so that processes can directly
access the memory allocated for it in the kernel.

remap_pfn_range is used instead of vm_insert_page due to aarch64
compatibility issues.

Signed-off-by: default avatarLorenz Bauer <lmb@isovalent.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Tested-by: default avatarAlan Maguire <alan.maguire@oracle.com>
Reviewed-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com
parent 8259eb0e

include/asm-generic/vmlinux.lds.h

+2 −1
Original line number Diff line number Diff line
@@ -667,10 +667,11 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) 
 */

#ifdef CONFIG_DEBUG_INFO_BTF

#define BTF								\

	. = ALIGN(PAGE_SIZE);						\

	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\

		BOUNDED_SECTION_BY(.BTF, _BTF)				\

	}								\

	. = ALIGN(4);							\

	. = ALIGN(PAGE_SIZE);						\

	.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {			\

		*(.BTF_ids)						\

	}

kernel/bpf/sysfs_btf.c

+32 −0
Original line number Diff line number Diff line
@@ -7,14 +7,46 @@ 
#include <linux/kobject.h>

#include <linux/init.h>

#include <linux/sysfs.h>

#include <linux/mm.h>

#include <linux/io.h>

#include <linux/btf.h>



/* See scripts/link-vmlinux.sh, gen_btf() func for details */

extern char __start_BTF[];

extern char __stop_BTF[];



static int btf_sysfs_vmlinux_mmap(struct file *filp, struct kobject *kobj,

				  const struct bin_attribute *attr,

				  struct vm_area_struct *vma)

{

	unsigned long pages = PAGE_ALIGN(attr->size) >> PAGE_SHIFT;

	size_t vm_size = vma->vm_end - vma->vm_start;

	phys_addr_t addr = virt_to_phys(__start_BTF);

	unsigned long pfn = addr >> PAGE_SHIFT;



	if (attr->private != __start_BTF || !PAGE_ALIGNED(addr))

		return -EINVAL;



	if (vma->vm_pgoff)

		return -EINVAL;



	if (vma->vm_flags & (VM_WRITE | VM_EXEC | VM_MAYSHARE))

		return -EACCES;



	if (pfn + pages < pfn)

		return -EINVAL;



	if ((vm_size >> PAGE_SHIFT) > pages)

		return -EINVAL;



	vm_flags_mod(vma, VM_DONTDUMP, VM_MAYEXEC | VM_MAYWRITE);

	return remap_pfn_range(vma, vma->vm_start, pfn, vm_size, vma->vm_page_prot);

}



static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {

	.attr = { .name = "vmlinux", .mode = 0444, },

	.read_new = sysfs_bin_attr_simple_read,

	.mmap = btf_sysfs_vmlinux_mmap,

};



struct kobject *btf_kobj;