Re: [PATCH 1/2] binfmt_elf_fdpic: support 64-bit systems

From: Palmer Dabbelt
Date: Tue Mar 21 2023 - 18:49:47 EST

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On Tue, 28 Feb 2023 05:51:25 PST (-0800), gerg@xxxxxxxxxx wrote:

The binfmt_flat_fdpic code has a number of 32-bit specific data
structures associated with it. Extend it to be able to support and
be used on 64-bit systems as well.

The new code defines a number of key 64-bit variants of the core
elf-fdpic data structures - along side the existing 32-bit sized ones.
A common set of generic named structures are defined to be either
the 32-bit or 64-bit ones as required at compile time. This is a
similar technique to that used in the ELF binfmt loader.

For example:

elf_fdpic_loadseg is either elf32_fdpic_loadseg or elf64_fdpic_loadseg
elf_fdpic_loadmap is either elf32_fdpic_loadmap or elf64_fdpic_loadmap

the choice based on ELFCLASS32 or ELFCLASS64.

Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxx>
---
fs/binfmt_elf_fdpic.c | 38 +++++++++++++++++-----------------
include/linux/elf-fdpic.h | 14 ++++++++++++-
include/uapi/linux/elf-fdpic.h | 15 ++++++++++++++
3 files changed, 47 insertions(+), 20 deletions(-)

Adding some of the binfmt/fs folks, who weren't directly on the mail. It's looking like we're generally OK with this in RISC-V land, though there's still no userspace posted. I don't think there's any rush here and it might be prudent to wait for userspace to start going through a bit of a review, but figured I'd at least poke everyone to see if there's any thoughts.

I'm fine either way, so
Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>

if that helps any. Also happy to take this through the RISC-V tree along with the other if that's easier, but again no rush.

diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index a05eafcacfb27..2eea6dd429fd6 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -138,7 +138,7 @@ static int is_constdisp(struct elfhdr *hdr)
static int elf_fdpic_fetch_phdrs(struct elf_fdpic_params *params,
struct file *file)
{
- struct elf32_phdr *phdr;
+ struct elf_phdr *phdr;
unsigned long size;
int retval, loop;
loff_t pos = params->hdr.e_phoff;
@@ -560,8 +560,8 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
sp &= ~7UL;

/* stack the load map(s) */
- len = sizeof(struct elf32_fdpic_loadmap);
- len += sizeof(struct elf32_fdpic_loadseg) * exec_params->loadmap->nsegs;
+ len = sizeof(struct elf_fdpic_loadmap);
+ len += sizeof(struct elf_fdpic_loadseg) * exec_params->loadmap->nsegs;
sp = (sp - len) & ~7UL;
exec_params->map_addr = sp;

@@ -571,8 +571,8 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
current->mm->context.exec_fdpic_loadmap = (unsigned long) sp;

if (interp_params->loadmap) {
- len = sizeof(struct elf32_fdpic_loadmap);
- len += sizeof(struct elf32_fdpic_loadseg) *
+ len = sizeof(struct elf_fdpic_loadmap);
+ len += sizeof(struct elf_fdpic_loadseg) *
interp_params->loadmap->nsegs;
sp = (sp - len) & ~7UL;
interp_params->map_addr = sp;
@@ -740,12 +740,12 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
struct mm_struct *mm,
const char *what)
{
- struct elf32_fdpic_loadmap *loadmap;
+ struct elf_fdpic_loadmap *loadmap;
#ifdef CONFIG_MMU
- struct elf32_fdpic_loadseg *mseg;
+ struct elf_fdpic_loadseg *mseg;
#endif
- struct elf32_fdpic_loadseg *seg;
- struct elf32_phdr *phdr;
+ struct elf_fdpic_loadseg *seg;
+ struct elf_phdr *phdr;
unsigned long load_addr, stop;
unsigned nloads, tmp;
size_t size;
@@ -767,7 +767,7 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,

params->loadmap = loadmap;

- loadmap->version = ELF32_FDPIC_LOADMAP_VERSION;
+ loadmap->version = ELF_FDPIC_LOADMAP_VERSION;
loadmap->nsegs = nloads;

load_addr = params->load_addr;
@@ -843,8 +843,8 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
if (phdr->p_vaddr >= seg->p_vaddr &&
phdr->p_vaddr + phdr->p_memsz <=
seg->p_vaddr + seg->p_memsz) {
- Elf32_Dyn __user *dyn;
- Elf32_Sword d_tag;
+ Elf_Dyn __user *dyn;
+ Elf_Sword d_tag;

params->dynamic_addr =
(phdr->p_vaddr - seg->p_vaddr) +
@@ -854,11 +854,11 @@ static int elf_fdpic_map_file(struct elf_fdpic_params *params,
* one item, and that the last item is a NULL
* entry */
if (phdr->p_memsz == 0 ||
- phdr->p_memsz % sizeof(Elf32_Dyn) != 0)
+ phdr->p_memsz % sizeof(Elf_Dyn) != 0)
goto dynamic_error;

- tmp = phdr->p_memsz / sizeof(Elf32_Dyn);
- dyn = (Elf32_Dyn __user *)params->dynamic_addr;
+ tmp = phdr->p_memsz / sizeof(Elf_Dyn);
+ dyn = (Elf_Dyn __user *)params->dynamic_addr;
if (get_user(d_tag, &dyn[tmp - 1].d_tag) ||
d_tag != 0)
goto dynamic_error;
@@ -927,8 +927,8 @@ static int elf_fdpic_map_file_constdisp_on_uclinux(
struct file *file,
struct mm_struct *mm)
{
- struct elf32_fdpic_loadseg *seg;
- struct elf32_phdr *phdr;
+ struct elf_fdpic_loadseg *seg;
+ struct elf_phdr *phdr;
unsigned long load_addr, base = ULONG_MAX, top = 0, maddr = 0;
int loop, ret;

@@ -1011,8 +1011,8 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
struct file *file,
struct mm_struct *mm)
{
- struct elf32_fdpic_loadseg *seg;
- struct elf32_phdr *phdr;
+ struct elf_fdpic_loadseg *seg;
+ struct elf_phdr *phdr;
unsigned long load_addr, delta_vaddr;
int loop, dvset;

diff --git a/include/linux/elf-fdpic.h b/include/linux/elf-fdpic.h
index 3bea95a1af537..e533f45131945 100644
--- a/include/linux/elf-fdpic.h
+++ b/include/linux/elf-fdpic.h
@@ -10,13 +10,25 @@

#include <uapi/linux/elf-fdpic.h>

+#if ELF_CLASS == ELFCLASS32
+#define Elf_Sword Elf32_Sword
+#define elf_fdpic_loadseg elf32_fdpic_loadseg
+#define elf_fdpic_loadmap elf32_fdpic_loadmap
+#define ELF_FDPIC_LOADMAP_VERSION ELF32_FDPIC_LOADMAP_VERSION
+#else
+#define Elf_Sword Elf64_Sxword
+#define elf_fdpic_loadmap elf64_fdpic_loadmap
+#define elf_fdpic_loadseg elf64_fdpic_loadseg
+#define ELF_FDPIC_LOADMAP_VERSION ELF64_FDPIC_LOADMAP_VERSION
+#endif
+
/*
* binfmt binary parameters structure
*/
struct elf_fdpic_params {
struct elfhdr hdr; /* ref copy of ELF header */
struct elf_phdr *phdrs; /* ref copy of PT_PHDR table */
- struct elf32_fdpic_loadmap *loadmap; /* loadmap to be passed to userspace */
+ struct elf_fdpic_loadmap *loadmap; /* loadmap to be passed to userspace */
unsigned long elfhdr_addr; /* mapped ELF header user address */
unsigned long ph_addr; /* mapped PT_PHDR user address */
unsigned long map_addr; /* mapped loadmap user address */
diff --git a/include/uapi/linux/elf-fdpic.h b/include/uapi/linux/elf-fdpic.h
index 4fcc6cfebe185..ec23f08711292 100644
--- a/include/uapi/linux/elf-fdpic.h
+++ b/include/uapi/linux/elf-fdpic.h
@@ -32,4 +32,19 @@ struct elf32_fdpic_loadmap {

#define ELF32_FDPIC_LOADMAP_VERSION 0x0000

+/* segment mappings for ELF FDPIC libraries/executables/interpreters */
+struct elf64_fdpic_loadseg {
+ Elf64_Addr addr; /* core address to which mapped */
+ Elf64_Addr p_vaddr; /* VMA recorded in file */
+ Elf64_Word p_memsz; /* allocation size recorded in file */
+};
+
+struct elf64_fdpic_loadmap {
+ Elf64_Half version; /* version of these structures, just in case... */
+ Elf64_Half nsegs; /* number of segments */
+ struct elf64_fdpic_loadseg segs[];
+};
+
+#define ELF64_FDPIC_LOADMAP_VERSION 0x0000
+
#endif /* _UAPI_LINUX_ELF_FDPIC_H */

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