[PATCH bpf-next 1/2] btf: allow mmap of vmlinux btf

[Lorenz Bauer]

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.

Signed-off-by: Lorenz Bauer <l...@isovalent.com>
---
 include/asm-generic/vmlinux.lds.h |  3 ++-
 kernel/bpf/sysfs_btf.c            | 25 +++++++++++++++++++++++--
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h 
b/include/asm-generic/vmlinux.lds.h
index 
58a635a6d5bdf0c53c267c2a3d21a5ed8678ce73..1750390735fac7637cc4d2fa05f96cb2a36aa448
 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -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)                                             \
        }
diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c
index 
81d6cf90584a7157929c50f62a5c6862e7a3d081..7651f37b82c78b8afd96078567a5b6612f5f4d97
 100644
--- a/kernel/bpf/sysfs_btf.c
+++ b/kernel/bpf/sysfs_btf.c
@@ -7,18 +7,39 @@
 #include <linux/kobject.h>
 #include <linux/init.h>
 #include <linux/sysfs.h>
+#include <linux/mm.h>
+#include <linux/io.h>
 
 /* See scripts/link-vmlinux.sh, gen_btf() func for details */
 extern char __start_BTF[];
 extern char __stop_BTF[];
 
+struct kobject *btf_kobj;
+
+static int btf_vmlinux_mmap(struct file *filp, struct kobject *kobj,
+                           const struct bin_attribute *attr,
+                           struct vm_area_struct *vma)
+{
+       size_t btf_size = __stop_BTF - __start_BTF;
+
+       if (kobj != btf_kobj)
+               return -EINVAL;
+
+       if (vma->vm_flags & (VM_WRITE|VM_EXEC|VM_MAYSHARE))
+               return -EACCES;
+
+       vm_flags_clear(vma, VM_MAYEXEC);
+       vm_flags_clear(vma, VM_MAYWRITE);
+
+       return vm_iomap_memory(vma, virt_to_phys(__start_BTF), btf_size);
+}
+
 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_vmlinux_mmap,
 };
 
-struct kobject *btf_kobj;
-
 static int __init btf_vmlinux_init(void)
 {
        bin_attr_btf_vmlinux.private = __start_BTF;

-- 
2.49.0