[PATCH bpf-next 2/3] bpf: Add size arg to build_id_parse function

Jiri Olsa
2021-01-14T13:42:10Z

It's possible to have other build id types (other than default SHA1).
Currently there's also ld support for MD5 build id.

Adding size argument to build_id_parse function, that returns (if defined)
size of the parsed build id, so we can recognize the build id type.

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/buildid.h | 3 ++-
kernel/bpf/stackmap.c | 2 +-
lib/buildid.c | 29 +++++++++++++++++++++--------
3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/include/linux/buildid.h b/include/linux/buildid.h
index 08028a212589..40232f90db6e 100644
--- a/include/linux/buildid.h
+++ b/include/linux/buildid.h
@@ -6,6 +6,7 @@

#define BUILD_ID_SIZE_MAX 20

-int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id);
+int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
+ __u32 *size);

#endif
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 55d254a59f07..cabaf7db8efc 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -189,7 +189,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,

for (i = 0; i < trace_nr; i++) {
vma = find_vma(current->mm, ips[i]);
- if (!vma || build_id_parse(vma, id_offs[i].build_id)) {
+ if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) {
/* per entry fall back to ips */
id_offs[i].status = BPF_STACK_BUILD_ID_IP;
id_offs[i].ip = ips[i];
diff --git a/lib/buildid.c b/lib/buildid.c
index 4a4f520c0e29..6156997c3895 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -12,6 +12,7 @@
*/
static inline int parse_build_id(void *page_addr,
unsigned char *build_id,
+ __u32 *size,
void *note_start,
Elf32_Word note_size)
{
@@ -38,6 +39,8 @@ static inline int parse_build_id(void *page_addr,
nhdr->n_descsz);
memset(build_id + nhdr->n_descsz, 0,
BUILD_ID_SIZE_MAX - nhdr->n_descsz);
+ if (size)
+ *size = nhdr->n_descsz;
return 0;
}
new_offs = note_offs + sizeof(Elf32_Nhdr) +
@@ -50,7 +53,8 @@ static inline int parse_build_id(void *page_addr,
}

/* Parse build ID from 32-bit ELF */
-static int get_build_id_32(void *page_addr, unsigned char *build_id)
+static int get_build_id_32(void *page_addr, unsigned char *build_id,
+ __u32 *size)
{
Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
Elf32_Phdr *phdr;
@@ -65,7 +69,7 @@ static int get_build_id_32(void *page_addr, unsigned char *build_id)

for (i = 0; i < ehdr->e_phnum; ++i) {
if (phdr[i].p_type == PT_NOTE &&
- !parse_build_id(page_addr, build_id,
+ !parse_build_id(page_addr, build_id, size,
page_addr + phdr[i].p_offset,
phdr[i].p_filesz))
return 0;
@@ -74,7 +78,8 @@ static int get_build_id_32(void *page_addr, unsigned char *build_id)
}

/* Parse build ID from 64-bit ELF */
-static int get_build_id_64(void *page_addr, unsigned char *build_id)
+static int get_build_id_64(void *page_addr, unsigned char *build_id,
+ __u32 *size)
{
Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
Elf64_Phdr *phdr;
@@ -89,7 +94,7 @@ static int get_build_id_64(void *page_addr, unsigned char *build_id)

for (i = 0; i < ehdr->e_phnum; ++i) {
if (phdr[i].p_type == PT_NOTE &&
- !parse_build_id(page_addr, build_id,
+ !parse_build_id(page_addr, build_id, size,
page_addr + phdr[i].p_offset,
phdr[i].p_filesz))
return 0;
@@ -97,8 +102,16 @@ static int get_build_id_64(void *page_addr, unsigned char *build_id)
return -EINVAL;
}

-/* Parse build ID of ELF file mapped to vma */
-int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id)
+/*
+ * Parse build ID of ELF file mapped to vma
+ * @vma: vma object
+ * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
+ * @size: returns actual build id size in case of success
+ *
+ * Returns 0 on success, otherwise error (< 0).
+ */
+int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
+ __u32 *size)
{
Elf32_Ehdr *ehdr;
struct page *page;
@@ -126,9 +139,9 @@ int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id)
goto out;

if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
- ret = get_build_id_32(page_addr, build_id);
+ ret = get_build_id_32(page_addr, build_id, size);
else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
- ret = get_build_id_64(page_addr, build_id);
+ ret = get_build_id_64(page_addr, build_id, size);
out:
kunmap_atomic(page_addr);
put_page(page);
--
2.26.2