Re: [PATCH] elf-load: Respect PT_GNU_STACK

[Sergey Bugaev]

On Wed, Mar 27, 2024 at 9:37 PM Samuel Thibault <samuel.thibault@gnu.org> wrote:
> But it's not getting used anywhere?

Indeed, I forgot to extract the kern/bootstrap.c part of the change.
Ooops :) Thanks for pointing it out.

Sergey

-- >8 --

If a bootstrap ELF contains a PT_GNU_STACK phdr, take stack protection
from there.  Otherwise, default to VM_PROT_ALL.
---
 include/mach/exec/elf.h  | 1 +
 include/mach/exec/exec.h | 2 ++
 kern/bootstrap.c         | 8 ++++----
 kern/elf-load.c          | 7 +++++++
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/include/mach/exec/elf.h b/include/mach/exec/elf.h
index 9e4f8f7e..55304496 100644
--- a/include/mach/exec/elf.h
+++ b/include/mach/exec/elf.h
@@ -300,6 +300,7 @@ typedef struct {
 #define PT_NOTE                4
 #define PT_SHLIB       5
 #define PT_PHDR                6
+#define PT_GNU_STACK   0x6474e551
 
 #define PT_LOPROC      0x70000000
 #define PT_HIPROC      0x7fffffff
diff --git a/include/mach/exec/exec.h b/include/mach/exec/exec.h
index 94b234b0..29fa897d 100644
--- a/include/mach/exec/exec.h
+++ b/include/mach/exec/exec.h
@@ -51,6 +51,8 @@ typedef struct exec_info
        /* (ELF) Address of interpreter string for loading shared libraries, 
null if none.  */
        vm_offset_t interp;
 
+       /* Required stack protection.  */
+       vm_prot_t stack_prot;
 } exec_info_t;
 
 typedef int exec_sectype_t;
diff --git a/kern/bootstrap.c b/kern/bootstrap.c
index 49358ac6..0470e1b6 100644
--- a/kern/bootstrap.c
+++ b/kern/bootstrap.c
@@ -620,10 +620,10 @@ build_args_and_stack(struct exec_info *boot_exec_info,
        stack_size = round_page(STACK_SIZE);
        stack_base = user_stack_low(stack_size);
 
-       (void) vm_allocate(current_task()->map,
-                       &stack_base,
-                       stack_size,
-                       FALSE);
+       (void) vm_map(current_map(), &stack_base, stack_size,
+                     0, FALSE, IP_NULL, 0, FALSE,
+                     boot_exec_info->stack_prot, VM_PROT_ALL,
+                     VM_INHERIT_DEFAULT);
 
        arg_pos = (char *)
                set_user_regs(stack_base, stack_size, boot_exec_info, arg_len);
diff --git a/kern/elf-load.c b/kern/elf-load.c
index ce86327c..596233a8 100644
--- a/kern/elf-load.c
+++ b/kern/elf-load.c
@@ -73,6 +73,8 @@ int exec_load(exec_read_func_t *read, exec_read_exec_func_t 
*read_exec,
        if (actual < phsize)
                return EX_CORRUPT;
 
+       out_info->stack_prot = VM_PROT_ALL;
+
        for (i = 0; i < x.e_phnum; i++)
        {
                ph = (Elf_Phdr *)((vm_offset_t)phdr + i * x.e_phentsize);
@@ -89,6 +91,11 @@ int exec_load(exec_read_func_t *read, exec_read_exec_func_t 
*read_exec,
                                              ph->p_vaddr + loadbase, 
ph->p_memsz, type);
                        if (result)
                                return result;
+               } else if (ph->p_type == PT_GNU_STACK) {
+                       out_info->stack_prot = 0;
+                       if (ph->p_flags & PF_R) out_info->stack_prot |= 
VM_PROT_READ;
+                       if (ph->p_flags & PF_W) out_info->stack_prot |= 
VM_PROT_WRITE;
+                       if (ph->p_flags & PF_X) out_info->stack_prot |= 
VM_PROT_EXECUTE;
                }
        }
 
-- 
2.44.0