* [PATCH] ELF: don't copy ELF header around
@ 2019-12-08 17:12 Alexey Dobriyan
2019-12-11 1:56 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Alexey Dobriyan @ 2019-12-08 17:12 UTC (permalink / raw)
To: akpm; +Cc: linux-kernel
ELF header is read into bprm->buf[] by generic execve code.
Save a memcpy and allocate just one header for the interpreter instead
of two headers (64 bytes instead of 128 on 64-bit).
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
fs/binfmt_elf.c | 55 +++++++++++++++++++++++++++----------------------------
1 file changed, 27 insertions(+), 28 deletions(-)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -161,8 +161,9 @@ static int padzero(unsigned long elf_bss)
#endif
static int
-create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
- unsigned long load_addr, unsigned long interp_load_addr)
+create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
+ unsigned long load_addr, unsigned long interp_load_addr,
+ unsigned long e_entry)
{
unsigned long p = bprm->p;
int argc = bprm->argc;
@@ -251,7 +252,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
NEW_AUX_ENT(AT_BASE, interp_load_addr);
NEW_AUX_ENT(AT_FLAGS, 0);
- NEW_AUX_ENT(AT_ENTRY, exec->e_entry);
+ NEW_AUX_ENT(AT_ENTRY, e_entry);
NEW_AUX_ENT(AT_UID, from_kuid_munged(cred->user_ns, cred->uid));
NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));
NEW_AUX_ENT(AT_GID, from_kgid_munged(cred->user_ns, cred->gid));
@@ -689,12 +690,13 @@ static int load_elf_binary(struct linux_binprm *bprm)
int bss_prot = 0;
int retval, i;
unsigned long elf_entry;
+ unsigned long e_entry;
unsigned long interp_load_addr = 0;
unsigned long start_code, end_code, start_data, end_data;
unsigned long reloc_func_desc __maybe_unused = 0;
int executable_stack = EXSTACK_DEFAULT;
+ struct elfhdr *elf_ex = (struct elfhdr *)bprm->buf;
struct {
- struct elfhdr elf_ex;
struct elfhdr interp_elf_ex;
} *loc;
struct arch_elf_state arch_state = INIT_ARCH_ELF_STATE;
@@ -705,30 +707,27 @@ static int load_elf_binary(struct linux_binprm *bprm)
retval = -ENOMEM;
goto out_ret;
}
-
- /* Get the exec-header */
- loc->elf_ex = *((struct elfhdr *)bprm->buf);
retval = -ENOEXEC;
/* First of all, some simple consistency checks */
- if (memcmp(loc->elf_ex.e_ident, ELFMAG, SELFMAG) != 0)
+ if (memcmp(elf_ex->e_ident, ELFMAG, SELFMAG) != 0)
goto out;
- if (loc->elf_ex.e_type != ET_EXEC && loc->elf_ex.e_type != ET_DYN)
+ if (elf_ex->e_type != ET_EXEC && elf_ex->e_type != ET_DYN)
goto out;
- if (!elf_check_arch(&loc->elf_ex))
+ if (!elf_check_arch(elf_ex))
goto out;
- if (elf_check_fdpic(&loc->elf_ex))
+ if (elf_check_fdpic(elf_ex))
goto out;
if (!bprm->file->f_op->mmap)
goto out;
- elf_phdata = load_elf_phdrs(&loc->elf_ex, bprm->file);
+ elf_phdata = load_elf_phdrs(elf_ex, bprm->file);
if (!elf_phdata)
goto out;
elf_ppnt = elf_phdata;
- for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
+ for (i = 0; i < elf_ex->e_phnum; i++, elf_ppnt++) {
char *elf_interpreter;
if (elf_ppnt->p_type != PT_INTERP)
@@ -782,7 +781,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
}
elf_ppnt = elf_phdata;
- for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++)
+ for (i = 0; i < elf_ex->e_phnum; i++, elf_ppnt++)
switch (elf_ppnt->p_type) {
case PT_GNU_STACK:
if (elf_ppnt->p_flags & PF_X)
@@ -792,7 +791,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
break;
case PT_LOPROC ... PT_HIPROC:
- retval = arch_elf_pt_proc(&loc->elf_ex, elf_ppnt,
+ retval = arch_elf_pt_proc(elf_ex, elf_ppnt,
bprm->file, false,
&arch_state);
if (retval)
@@ -836,7 +835,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
* still possible to return an error to the code that invoked
* the exec syscall.
*/
- retval = arch_check_elf(&loc->elf_ex,
+ retval = arch_check_elf(elf_ex,
!!interpreter, &loc->interp_elf_ex,
&arch_state);
if (retval)
@@ -849,8 +848,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
/* Do this immediately, since STACK_TOP as used in setup_arg_pages
may depend on the personality. */
- SET_PERSONALITY2(loc->elf_ex, &arch_state);
- if (elf_read_implies_exec(loc->elf_ex, executable_stack))
+ SET_PERSONALITY2(*elf_ex, &arch_state);
+ if (elf_read_implies_exec(*elf_ex, executable_stack))
current->personality |= READ_IMPLIES_EXEC;
if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
@@ -877,7 +876,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
/* Now we do a little grungy work by mmapping the ELF image into
the correct location in memory. */
for(i = 0, elf_ppnt = elf_phdata;
- i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
+ i < elf_ex->e_phnum; i++, elf_ppnt++) {
int elf_prot, elf_flags;
unsigned long k, vaddr;
unsigned long total_size = 0;
@@ -921,9 +920,9 @@ static int load_elf_binary(struct linux_binprm *bprm)
* If we are loading ET_EXEC or we have already performed
* the ET_DYN load_addr calculations, proceed normally.
*/
- if (loc->elf_ex.e_type == ET_EXEC || load_addr_set) {
+ if (elf_ex->e_type == ET_EXEC || load_addr_set) {
elf_flags |= MAP_FIXED;
- } else if (loc->elf_ex.e_type == ET_DYN) {
+ } else if (elf_ex->e_type == ET_DYN) {
/*
* This logic is run once for the first LOAD Program
* Header for ET_DYN binaries to calculate the
@@ -972,7 +971,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
load_bias = ELF_PAGESTART(load_bias - vaddr);
total_size = total_mapping_size(elf_phdata,
- loc->elf_ex.e_phnum);
+ elf_ex->e_phnum);
if (!total_size) {
retval = -EINVAL;
goto out_free_dentry;
@@ -990,7 +989,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
if (!load_addr_set) {
load_addr_set = 1;
load_addr = (elf_ppnt->p_vaddr - elf_ppnt->p_offset);
- if (loc->elf_ex.e_type == ET_DYN) {
+ if (elf_ex->e_type == ET_DYN) {
load_bias += error -
ELF_PAGESTART(load_bias + vaddr);
load_addr += load_bias;
@@ -1031,7 +1030,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
}
}
- loc->elf_ex.e_entry += load_bias;
+ e_entry = elf_ex->e_entry + load_bias;
elf_bss += load_bias;
elf_brk += load_bias;
start_code += load_bias;
@@ -1074,7 +1073,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
allow_write_access(interpreter);
fput(interpreter);
} else {
- elf_entry = loc->elf_ex.e_entry;
+ elf_entry = e_entry;
if (BAD_ADDR(elf_entry)) {
retval = -EINVAL;
goto out_free_dentry;
@@ -1092,8 +1091,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
goto out;
#endif /* ARCH_HAS_SETUP_ADDITIONAL_PAGES */
- retval = create_elf_tables(bprm, &loc->elf_ex,
- load_addr, interp_load_addr);
+ retval = create_elf_tables(bprm, elf_ex,
+ load_addr, interp_load_addr, e_entry);
if (retval < 0)
goto out;
current->mm->end_code = end_code;
@@ -1111,7 +1110,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
* growing down), and into the unused ELF_ET_DYN_BASE region.
*/
if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) &&
- loc->elf_ex.e_type == ET_DYN && !interpreter)
+ elf_ex->e_type == ET_DYN && !interpreter)
current->mm->brk = current->mm->start_brk =
ELF_ET_DYN_BASE;
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ELF: don't copy ELF header around
2019-12-08 17:12 [PATCH] ELF: don't copy ELF header around Alexey Dobriyan
@ 2019-12-11 1:56 ` Andrew Morton
2019-12-11 7:19 ` Alexey Dobriyan
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2019-12-11 1:56 UTC (permalink / raw)
To: Alexey Dobriyan; +Cc: linux-kernel
On Sun, 8 Dec 2019 20:12:42 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> ELF header is read into bprm->buf[] by generic execve code.
>
> Save a memcpy and allocate just one header for the interpreter instead
> of two headers (64 bytes instead of 128 on 64-bit).
Hard to review. Why were there two copies in the first place? Because
of the need to modify the caller's version when we do
`loc->elf_ex.e_entry += load_bias', yes? Any other place?
Local variable `loc' can go away now, yes?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] ELF: don't copy ELF header around
2019-12-11 1:56 ` Andrew Morton
@ 2019-12-11 7:19 ` Alexey Dobriyan
0 siblings, 0 replies; 3+ messages in thread
From: Alexey Dobriyan @ 2019-12-11 7:19 UTC (permalink / raw)
To: Andrew Morton; +Cc: linux-kernel
On Tue, Dec 10, 2019 at 05:56:11PM -0800, Andrew Morton wrote:
> On Sun, 8 Dec 2019 20:12:42 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
> > ELF header is read into bprm->buf[] by generic execve code.
> >
> > Save a memcpy and allocate just one header for the interpreter instead
> > of two headers (64 bytes instead of 128 on 64-bit).
>
> Hard to review. Why were there two copies in the first place?
That's a good question. Both can live on stack in fact
but [rsp+disp32] addressing generates a lot of bloat (few KB).
> Because of the need to modify the caller's version when we do
> `loc->elf_ex.e_entry += load_bias', yes? Any other place?
No, but I'll double check. It was written this way presumably to not
allocate one more stack variable.
> Local variable `loc' can go away now, yes?
It can.
I have big plans to get rid of all allocations in the common case
and "fetch" headers from pagecache. This is why all headers better to be
"const" which this patch partially progresses to.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-12-11 7:19 UTC | newest]
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2019-12-11 1:56 ` Andrew Morton
2019-12-11 7:19 ` Alexey Dobriyan
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