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authorChris Kennelly <ckennelly@google.com>2020-10-15 20:12:32 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-10-16 11:11:21 -0700
commitce81bb256a224259ab686742a6284930cbe4f1fa (patch)
tree28ae24498b302b099b95cc5b04ed434fed1bb527
parent48ca2d8ac8a1d404a0f85eabfe1546304adbd844 (diff)
fs/binfmt_elf: use PT_LOAD p_align values for suitable start address
Patch series "Selecting Load Addresses According to p_align", v3. 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. While specifying -z,max-page-size=0x200000 to the linker will generate suitably aligned segments for huge pages on x86_64, the executable needs to be loaded at a suitably aligned address as well. This alignment requires the binary's cooperation, as distinct segments need to be appropriately paddded to be eligible for THP. For binaries built with increased alignment, this limits the number of bits usable for ASLR, but provides some randomization over using fixed load addresses/non-PIE binaries. This patch (of 2): 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. For binaries built with increased alignment, this limits the number of bits usable for ASLR, but provides some randomization over using fixed load addresses/non-PIE binaries. Tested by verifying program with -Wl,-z,max-page-size=0x200000 loading. [akpm@linux-foundation.org: fix max() warning] [ckennelly@google.com: augment comment] Link: https://lkml.kernel.org/r/20200821233848.3904680-2-ckennelly@google.com Signed-off-by: Chris Kennelly <ckennelly@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Song Liu <songliubraving@fb.com> Cc: David Rientjes <rientjes@google.com> Cc: Ian Rogers <irogers@google.com> Cc: Hugh Dickens <hughd@google.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Sandeep Patil <sspatil@google.com> Cc: Fangrui Song <maskray@google.com> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Shuah Khan <shuah@kernel.org> Link: https://lkml.kernel.org/r/20200820170541.1132271-1-ckennelly@google.com Link: https://lkml.kernel.org/r/20200820170541.1132271-2-ckennelly@google.com Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/binfmt_elf.c25
1 files changed, 25 insertions, 0 deletions
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 13d053982dd7..96370e3e3687 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -13,6 +13,7 @@
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
+#include <linux/log2.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/errno.h>
@@ -421,6 +422,26 @@ 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) {
+ unsigned long p_align = cmds[i].p_align;
+
+ /* skip non-power of two alignments as invalid */
+ if (!is_power_of_2(p_align))
+ continue;
+ alignment = max(alignment, 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
@@ -1008,6 +1029,7 @@ out_free_interp:
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;
@@ -1086,6 +1108,9 @@ out_free_interp:
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;