[PATCH v5 bpf-next 04/10] lib/buildid: remove single-page limit for PHDR search

Andrii Nakryiko
2024-08-13T00:29:52Z

Now that freader allows to access multiple pages transparently, there is
no need to limit program headers to the very first ELF file page. Remove
this limitation, but still put some sane limit on amount of program
headers that we are willing to iterate over (set arbitrarily to 256).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
lib/buildid.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/buildid.c b/lib/buildid.c
index abf5d1c7eb47..8296428ff82f 100644
--- a/lib/buildid.c
+++ b/lib/buildid.c
@@ -8,6 +8,8 @@

#define BUILD_ID 3

+#define MAX_PHDR_CNT 256
+
struct freader {
void *buf;
u32 buf_sz;
@@ -223,9 +225,9 @@ static int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *si
phnum = READ_ONCE(ehdr->e_phnum);
phoff = READ_ONCE(ehdr->e_phoff);

- /* only supports phdr that fits in one page */
- if (phnum > (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
- return -EINVAL;
+ /* set upper bound on amount of segments (phdrs) we iterate */
+ if (phnum > MAX_PHDR_CNT)
+ phnum = MAX_PHDR_CNT;

/* check that phoff is not large enough to cause an overflow */
if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)
@@ -260,9 +262,9 @@ static int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *si
phnum = READ_ONCE(ehdr->e_phnum);
phoff = READ_ONCE(ehdr->e_phoff);

- /* only supports phdr that fits in one page */
- if (phnum > (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
- return -EINVAL;
+ /* set upper bound on amount of segments (phdrs) we iterate */
+ if (phnum > MAX_PHDR_CNT)
+ phnum = MAX_PHDR_CNT;

/* check that phoff is not large enough to cause an overflow */
if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)
--
2.43.5