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btf: Allow mmap of vmlinux btf

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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: Lorenz Bauer <lmb@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Link: https://lore.kernel.org/bpf/20250520-vmlinux-mmap-v5-1-e8c941acc414@isovalent.com
This commit is contained in:
Lorenz Bauer 2025-05-20 14:01:17 +01:00 • committed by Andrii Nakryiko
parent 8259eb0e06
commit a539e2a6d5
2 changed files with 34 additions and 1 deletions
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3
include/asm-generic/vmlinux.lds.h
View file

@ -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) \
}

32
kernel/bpf/sysfs_btf.c
View file

@ -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;