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Split the old READ_IMPLIES_EXEC workaround from executable PT_GNU_STACK

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now that toolchains long support PT_GNU_STACK marking and there's no
 need anymore to force modern programs into having all its user mappings
 executable instead of only the stack and the PROT_EXEC ones. Disable
 that automatic READ_IMPLIES_EXEC forcing on x86-64 and arm64. Add tables
 documenting how READ_IMPLIES_EXEC is handled on x86-64, arm and arm64.
 By Kees Cook.
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Merge tag 'core_core_updates_for_5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull READ_IMPLIES_EXEC changes from Borislav Petkov:
 "Split the old READ_IMPLIES_EXEC workaround from executable
  PT_GNU_STACK now that toolchains long support PT_GNU_STACK marking and
  there's no need anymore to force modern programs into having all its
  user mappings executable instead of only the stack and the PROT_EXEC
  ones.

  Disable that automatic READ_IMPLIES_EXEC forcing on x86-64 and
  arm64.

  Add tables documenting how READ_IMPLIES_EXEC is handled on x86-64, arm
  and arm64.

  By Kees Cook"

* tag 'core_core_updates_for_5.8' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  arm64/elf: Disable automatic READ_IMPLIES_EXEC for 64-bit address spaces
  arm32/64/elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK
  arm32/64/elf: Add tables to document READ_IMPLIES_EXEC
  x86/elf: Disable automatic READ_IMPLIES_EXEC on 64-bit
  x86/elf: Split READ_IMPLIES_EXEC from executable PT_GNU_STACK
  x86/elf: Add table to document READ_IMPLIES_EXEC
This commit is contained in:
Linus Torvalds 2020-06-05 13:45:21 -07:00
commit ac7b34218a
4 changed files with 71 additions and 6 deletions
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27
arch/arm/kernel/elf.c
View File

@ -78,13 +78,32 @@ void elf_set_personality(const struct elf32_hdr *x)
EXPORT_SYMBOL(elf_set_personality);
/*
* Set READ_IMPLIES_EXEC if:
* - the binary requires an executable stack
* - we're running on a CPU which doesn't support NX.
* An executable for which elf_read_implies_exec() returns TRUE will
* have the READ_IMPLIES_EXEC personality flag set automatically.
*
* The decision process for determining the results are:
*
*              CPU: | lacks NX*  | has NX |
* ELF:              |            |           |
* ---------------------|------------|------------|
* missing PT_GNU_STACK | exec-all   | exec-all  |
* PT_GNU_STACK == RWX  | exec-all   | exec-stack |
* PT_GNU_STACK == RW   | exec-all  | exec-none |
*
* exec-all : all PROT_READ user mappings are executable, except when
* backed by files on a noexec-filesystem.
* exec-none : only PROT_EXEC user mappings are executable.
* exec-stack: only the stack and PROT_EXEC user mappings are executable.
*
* *this column has no architectural effect: NX markings are ignored by
* hardware, but may have behavioral effects when "wants X" collides with
* "cannot be X" constraints in memory permission flags, as in
* https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
*
*/
int arm_elf_read_implies_exec(int executable_stack)
{
if (executable_stack != EXSTACK_DISABLE_X)
if (executable_stack == EXSTACK_DEFAULT)
return 1;
if (cpu_architecture() < CPU_ARCH_ARMv6)
return 1;

23
arch/arm64/include/asm/elf.h
View File

@ -96,7 +96,28 @@
*/
#define elf_check_arch(x) ((x)->e_machine == EM_AARCH64)
#define elf_read_implies_exec(ex,stk) (stk != EXSTACK_DISABLE_X)
/*
* An executable for which elf_read_implies_exec() returns TRUE will
* have the READ_IMPLIES_EXEC personality flag set automatically.
*
* The decision process for determining the results are:
*
*              CPU*: | arm32    | arm64 |
* ELF:              |            |            |
* ---------------------|------------|------------|
* missing PT_GNU_STACK | exec-all   | exec-none  |
* PT_GNU_STACK == RWX  | exec-stack | exec-stack |
* PT_GNU_STACK == RW   | exec-none | exec-none |
*
* exec-all : all PROT_READ user mappings are executable, except when
* backed by files on a noexec-filesystem.
* exec-none : only PROT_EXEC user mappings are executable.
* exec-stack: only the stack and PROT_EXEC user mappings are executable.
*
* *all arm64 CPUs support NX, so there is no "lacks NX" column.
*
*/
#define compat_elf_read_implies_exec(ex, stk) (stk == EXSTACK_DEFAULT)
#define CORE_DUMP_USE_REGSET
#define ELF_EXEC_PAGESIZE PAGE_SIZE

22
arch/x86/include/asm/elf.h
View File

@ -281,9 +281,29 @@ extern u32 elf_hwcap2;
/*
* An executable for which elf_read_implies_exec() returns TRUE will
* have the READ_IMPLIES_EXEC personality flag set automatically.
*
* The decision process for determining the results are:
*
*              CPU: | lacks NX*  | has NX, ia32     | has NX, x86_64 |
* ELF:              |            |                  |                |
* ---------------------|------------|------------------|----------------|
* missing PT_GNU_STACK | exec-all   | exec-all         | exec-none      |
* PT_GNU_STACK == RWX  | exec-stack | exec-stack       | exec-stack     |
* PT_GNU_STACK == RW   | exec-none  | exec-none        | exec-none      |
*
* exec-all : all PROT_READ user mappings are executable, except when
* backed by files on a noexec-filesystem.
* exec-none : only PROT_EXEC user mappings are executable.
* exec-stack: only the stack and PROT_EXEC user mappings are executable.
*
* *this column has no architectural effect: NX markings are ignored by
* hardware, but may have behavioral effects when "wants X" collides with
* "cannot be X" constraints in memory permission flags, as in
* https://lkml.kernel.org/r/20190418055759.GA3155@mellanox.com
*
*/
#define elf_read_implies_exec(ex, executable_stack) \
(executable_stack != EXSTACK_DISABLE_X)
(mmap_is_ia32() && executable_stack == EXSTACK_DEFAULT)
struct task_struct;

5
fs/compat_binfmt_elf.c
View File

@ -117,6 +117,11 @@
#define arch_setup_additional_pages compat_arch_setup_additional_pages
#endif
#ifdef compat_elf_read_implies_exec
#undef elf_read_implies_exec
#define elf_read_implies_exec compat_elf_read_implies_exec
#endif
/*
* Rename a few of the symbols that binfmt_elf.c will define.
* These are all local so the names don't really matter, but it