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um: Create signal stack memory assignment in stub_data

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When we switch to use seccomp, we need both the signal stack and other
data (i.e. syscall information) to co-exist in the stub data. To
facilitate this, start by defining separate memory areas for the stack
and syscall data.

This moves the signal stack onto a new page as the memory area is not
sufficient to hold both signal stack and syscall information.

Only change the signal stack setup for now, as the syscall code will be
reworked later.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Link: https://patch.msgid.link/20240703134536.1161108-3-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
This commit is contained in:
Benjamin Berg 2024-07-03 15:45:26 +02:00 committed by Johannes Berg
parent d1d3a2e69b
commit dc26184a9d
5 changed files with 24 additions and 8 deletions
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2
arch/um/include/shared/as-layout.h
View File

@ -23,7 +23,7 @@
#define STUB_START stub_start
#define STUB_CODE STUB_START
#define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
#define STUB_DATA_PAGES 1 /* must be a power of two */
#define STUB_DATA_PAGES 2 /* must be a power of two */
#define STUB_END (STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE)
#ifndef __ASSEMBLY__

9
arch/um/include/shared/skas/stub-data.h
View File

@ -8,10 +8,19 @@
#ifndef __STUB_DATA_H
#define __STUB_DATA_H
#include <linux/compiler_types.h>
#include <as-layout.h>
struct stub_data {
unsigned long offset;
int fd;
long parent_err, child_err;
/* 128 leaves enough room for additional fields in the struct */
unsigned char syscall_data[UM_KERN_PAGE_SIZE - 128] __aligned(16);
/* Stack for our signal handlers and for calling into . */
unsigned char sigstack[UM_KERN_PAGE_SIZE] __aligned(UM_KERN_PAGE_SIZE);
};
#endif

6
arch/um/kernel/skas/clone.c
View File

@ -27,9 +27,11 @@ stub_clone_handler(void)
struct stub_data *data = get_stub_data();
long err;
/* syscall data as a temporary stack area (bottom half). */
err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
(unsigned long)data +
STUB_DATA_PAGES * UM_KERN_PAGE_SIZE / 2);
(unsigned long) data->syscall_data +
sizeof(data->syscall_data) / 2 -
sizeof(void *));
if (err) {
data->parent_err = err;
goto done;

4
arch/um/kernel/skas/mmu.c
View File

@ -14,6 +14,10 @@
#include <as-layout.h>
#include <os.h>
#include <skas.h>
#include <stub-data.h>
/* Ensure the stub_data struct covers the allocated area */
static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
int init_new_context(struct task_struct *task, struct mm_struct *mm)
{

11
arch/um/os-Linux/skas/process.c
View File

@ -474,11 +474,12 @@ static int __init init_thread_regs(void)
thread_regs[REGS_IP_INDEX] = STUB_CODE +
(unsigned long) stub_clone_handler -
(unsigned long) __syscall_stub_start;
thread_regs[REGS_SP_INDEX] = STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE -
sizeof(void *);
#ifdef __SIGNAL_FRAMESIZE
thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
#endif
/* syscall data as a temporary stack area (top half). */
thread_regs[REGS_SP_INDEX] = STUB_DATA +
offsetof(struct stub_data, syscall_data) +
sizeof(((struct stub_data *) 0)->syscall_data) -
sizeof(void *);
return 0;
}