fs/binfmt_elf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
From: Yin Fengwei <fengwei_yin@linux.alibaba.com>
We have assembly code generated by a script. GCC successfully compiles
it. However, the kernel cannot load it on an ARM64 platform with a 4K
page size. In contrast, the same ELF file loads correctly on the same
platform with a 64K page size.
The root cause is the Linux kernel's ELF_MIN_ALIGN limitation on the
program headers of ELF files. The ELF file contains 78 program headers
(the script inserts many holes when generating the assembly code). On
ARM64 with a 4K page size, the ELF_MIN_ALLIGN enforces a maximum of 74
program headers, causing the ELF file to fail. However, with a 64K page
size, the ELF_MIN_ALIGN is relaxed to over 1,184 program headers, allowing
the file to run correctly.
Cook kindly identified that this limitation was introduced in
Linux-0.99.15f without an explanation for its purpose [1].
The ELF specification does not impose such a restriction on program
headers. Removing the ELF_MIN_ALIGN limitation on program headers to
align with the ELF spec. After removing ELF_MIN_ALIGN limitation,
64K size limitation still exist which should be sufficient.
[1] https://lore.kernel.org/linux-mm/202506270854.A729825@keescook/
Originally-by: Kees Cook <kees@kernel.org>
Signed-off-by: Yin Fengwei <fengwei_yin@linux.alibaba.com>
---
Explaination about "Originally-by": it's debug code from Cook. And
he didn't show the intention to submit it as patch. The change did
fix the issue I hit...
fs/binfmt_elf.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index a43363d593e5..1cb35a2bc528 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -519,7 +519,7 @@ static struct elf_phdr *load_elf_phdrs(const struct elfhdr *elf_ex,
/* Sanity check the number of program headers... */
/* ...and their total size. */
size = sizeof(struct elf_phdr) * elf_ex->e_phnum;
- if (size == 0 || size > 65536 || size > ELF_MIN_ALIGN)
+ if (size == 0 || size > 65536)
goto out;
elf_phdata = kmalloc(size, GFP_KERNEL);
--
2.49.0On Thu, 17 Jul 2025 19:01:08 +0800, fengwei_yin@linux.alibaba.com wrote:
> We have assembly code generated by a script. GCC successfully compiles
> it. However, the kernel cannot load it on an ARM64 platform with a 4K
> page size. In contrast, the same ELF file loads correctly on the same
> platform with a 64K page size.
>
> The root cause is the Linux kernel's ELF_MIN_ALIGN limitation on the
> program headers of ELF files. The ELF file contains 78 program headers
> (the script inserts many holes when generating the assembly code). On
> ARM64 with a 4K page size, the ELF_MIN_ALLIGN enforces a maximum of 74
> program headers, causing the ELF file to fail. However, with a 64K page
> size, the ELF_MIN_ALIGN is relaxed to over 1,184 program headers, allowing
> the file to run correctly.
>
> [...]
Applied to for-next/execve, thanks!
[1/1] binfmt_elf: remove the 4k limitation of program header size
https://git.kernel.org/kees/c/8030790477e8
Take care,
--
Kees Cook
On Thu, Jul 17, 2025 at 04:31:50PM +0800, Kees Cook wrote: > On Thu, 17 Jul 2025 19:01:08 +0800, fengwei_yin@linux.alibaba.com wrote: > > We have assembly code generated by a script. GCC successfully compiles > > it. However, the kernel cannot load it on an ARM64 platform with a 4K > > page size. In contrast, the same ELF file loads correctly on the same > > platform with a 64K page size. > > > > The root cause is the Linux kernel's ELF_MIN_ALIGN limitation on the > > program headers of ELF files. The ELF file contains 78 program headers > > (the script inserts many holes when generating the assembly code). On > > ARM64 with a 4K page size, the ELF_MIN_ALLIGN enforces a maximum of 74 > > program headers, causing the ELF file to fail. However, with a 64K page > > size, the ELF_MIN_ALIGN is relaxed to over 1,184 program headers, allowing > > the file to run correctly. > > > > [...] > > Applied to for-next/execve, thanks! Cook, thanks a lot. Regards Yin, Fengwei > > [1/1] binfmt_elf: remove the 4k limitation of program header size > https://git.kernel.org/kees/c/8030790477e8 > > Take care, > > -- > Kees Cook
On Sat, Jul 19, 2025 at 17:17:09 +0800, YinFengwei wrote: > On Thu, Jul 17, 2025 at 04:31:50PM +0800, Kees Cook wrote: > > On Thu, 17 Jul 2025 19:01:08 +0800, fengwei_yin@linux.alibaba.com wrote: > > > We have assembly code generated by a script. GCC successfully compiles > > > it. However, the kernel cannot load it on an ARM64 platform with a 4K > > > page size. In contrast, the same ELF file loads correctly on the same > > > platform with a 64K page size. > > > > > > The root cause is the Linux kernel's ELF_MIN_ALIGN limitation on the > > > program headers of ELF files. The ELF file contains 78 program headers > > > (the script inserts many holes when generating the assembly code). On > > > ARM64 with a 4K page size, the ELF_MIN_ALLIGN enforces a maximum of 74 > > > program headers, causing the ELF file to fail. However, with a 64K page > > > size, the ELF_MIN_ALIGN is relaxed to over 1,184 program headers, allowing > > > the file to run correctly. > > > > > > [...] > > > > Applied to for-next/execve, thanks! > Cook, thanks a lot. > > Regards > Yin, Fengwei > > > > > [1/1] binfmt_elf: remove the 4k limitation of program header size > > https://git.kernel.org/kees/c/8030790477e8 > > > > Take care, Hi, I noticed this removal and wonder whether it could be a problem on smaller platforms. IIRC that code has been there since ELF support was added in one form or another; and the idea behind it was to simplify the code by ensuring no cross-page reads could happen, as these could cause undefined behaviours or read abort exceptions. Best regards.
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