Merge branch 'allow-mmap-of-sys-kernel-btf-vmlinux'

Lorenz Bauer says:

====================
Allow mmap of /sys/kernel/btf/vmlinux

I'd like to cut down the memory usage of parsing vmlinux BTF in ebpf-go.
With some upcoming changes the library is sitting at 5MiB for a parse.
Most of that memory is simply copying the BTF blob into user space.
By allowing vmlinux BTF to be mmapped read-only into user space I can
cut memory usage by about 75%.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
---
Changes in v5:
- Fix error return of btf_parse_raw_mmap (Andrii)
- Link to v4: https://lore.kernel.org/r/20250510-vmlinux-mmap-v4-0-69e424b2a672@isovalent.com

Changes in v4:
- Go back to remap_pfn_range for aarch64 compat
- Dropped btf_new_no_copy (Andrii)
- Fixed nits in selftests (Andrii)
- Clearer error handling in the mmap handler (Andrii)
- Fixed build on s390
- Link to v3: https://lore.kernel.org/r/20250505-vmlinux-mmap-v3-0-5d53afa060e8@isovalent.com

Changes in v3:
- Remove slightly confusing calculation of trailing (Alexei)
- Use vm_insert_page (Alexei)
- Simplified libbpf code
- Link to v2: https://lore.kernel.org/r/20250502-vmlinux-mmap-v2-0-95c271434519@isovalent.com

Changes in v2:
- Use btf__new in selftest
- Avoid vm_iomap_memory in btf_vmlinux_mmap
- Add VM_DONTDUMP
- Add support to libbpf
- Link to v1: https://lore.kernel.org/r/20250501-vmlinux-mmap-v1-0-aa2724572598@isovalent.com

---
====================

Link: https://patch.msgid.link/20250520-vmlinux-mmap-v5-0-e8c941acc414@isovalent.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 81d6cf90584a..941d0d2427e3 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -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;