lib/buildid: rename build_id_parse() into build_id_parse_nofault()

Make it clear that build_id_parse() assumes that it can take no page
fault by renaming it and current few users to build_id_parse_nofault().

Also add build_id_parse() stub which for now falls back to non-sleepable
implementation, but will be changed in subsequent patches to take
advantage of sleepable context. PROCMAP_QUERY ioctl() on
/proc/<pid>/maps file is using build_id_parse() and will automatically
take advantage of more reliable sleepable context implementation.

Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20240829174232.3133883-6-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/buildid.h b/include/linux/buildid.h
index 20aa3c2d89f760a28e57d03bfd3baf62b560f61c..014a88c410739e6dc4a6feae390653990baf06b7 100644 (file)
--- a/include/linux/buildid.h
+++ b/include/linux/buildid.h
@@ -7,8 +7,8 @@
 #define BUILD_ID_SIZE_MAX 20
 
 struct vm_area_struct;
-int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
-                  __u32 *size);
+int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size);
+int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size);
 int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size);
 
 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index c99f8e5234ac484a48506249b392d520aefe5a85..770ae8e880168f354cbc9cac5263105d2564677b 100644 (file)
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -156,7 +156,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
                        goto build_id_valid;
                }
                vma = find_vma(current->mm, ips[i]);
-               if (!vma || build_id_parse(vma, id_offs[i].build_id, NULL)) {
+               if (!vma || build_id_parse_nofault(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/kernel/events/core.c b/kernel/events/core.c
index c973e3c11e036f6ed948431f95ebafab5011663f..c78a77f9dce4f01d92284acfccc7a2400141482e 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8851,7 +8851,7 @@ got_name:
        mmap_event->event_id.header.size = sizeof(mmap_event->event_id) + size;
 
        if (atomic_read(&nr_build_id_events))
-               build_id_parse(vma, mmap_event->build_id, &mmap_event->build_id_size);
+               build_id_parse_nofault(vma, mmap_event->build_id, &mmap_event->build_id_size);
 
        perf_iterate_sb(perf_event_mmap_output,
                       mmap_event,

diff --git a/lib/buildid.c b/lib/buildid.c
index e8fc4aeb01f2d28e06fc697eb8a6b6facf84c120..c1cbd34f36859ff182b3a18d62fb48d20b69012c 100644 (file)
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -293,10 +293,12 @@ static int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *si
  * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
  * @size:     returns actual build id size in case of success
  *
- * Return: 0 on success, -EINVAL otherwise
+ * Assumes no page fault can be taken, so if relevant portions of ELF file are
+ * not already paged in, fetching of build ID fails.
+ *
+ * Return: 0 on success; negative error, otherwise
  */
-int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
-                  __u32 *size)
+int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
 {
        const Elf32_Ehdr *ehdr;
        struct freader r;
@@ -335,6 +337,23 @@ out:
        return ret;
 }
 
+/*
+ * 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
+ *
+ * Assumes faultable context and can cause page faults to bring in file data
+ * into page cache.
+ *
+ * Return: 0 on success; negative error, otherwise
+ */
+int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
+{
+       /* fallback to non-faultable version for now */
+       return build_id_parse_nofault(vma, build_id, size);
+}
+
 /**
  * build_id_parse_buf - Get build ID from a buffer
  * @buf:      ELF note section(s) to parse