The current ELF loading mechancism provides page-aligned mappings. This
can lead to the program being loaded in a way unsuitable for
file-backed, transparent huge pages when handling PIE executables.
Tested: verified program with -Wl,-z,max-page-size=0x200000 loading
Signed-off-by: Chris Kennelly <ckennelly@xxxxxxxxxx>
---
fs/binfmt_elf.c | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index f4713ea76e827..83fadf66d25ef 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -418,6 +418,25 @@ static int elf_read(struct file *file, void *buf, size_t len, loff_t pos)
return 0;
}
+static unsigned long maximum_alignment(struct elf_phdr *cmds, int nr)
+{
+ unsigned long alignment = 0;
+ int i;
+
+ for (i = 0; i < nr; i++) {
+ if (cmds[i].p_type == PT_LOAD) {
+ /* skip non-power of two alignments */
+ if (cmds[i].p_align & (cmds[i].p_align - 1))
+ continue;
+ if (cmds[i].p_align > alignment)
+ alignment = cmds[i].p_align;
+ }
+ }
+
+ /* ensure we align to at least one page */
+ return ELF_PAGEALIGN(alignment);
+}
+
/**
* load_elf_phdrs() - load ELF program headers
* @elf_ex: ELF header of the binary whose program headers should be loaded
@@ -883,6 +902,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
int elf_prot, elf_flags;
unsigned long k, vaddr;
unsigned long total_size = 0;
+ unsigned long alignment;
if (elf_ppnt->p_type != PT_LOAD)
continue;
@@ -960,6 +980,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
load_bias = ELF_ET_DYN_BASE;
if (current->flags & PF_RANDOMIZE)
load_bias += arch_mmap_rnd();
+ alignment = maximum_alignment(
+ elf_phdata, elf_ex->e_phnum);
+ if (alignment)
+ load_bias &= ~(alignment - 1);
elf_flags |= MAP_FIXED;
} else
load_bias = 0;
--
2.28.0.rc0.105.gf9edc3c819-goog
