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Subject[PATCH] ELF: don't copy ELF header around
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;

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