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x86: Rewrite ret_from_fork() in C

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When kCFI is enabled, special handling is needed for the indirect call
to the kernel thread function.  Rewrite the ret_from_fork() function in
C so that the compiler can properly handle the indirect call.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lkml.kernel.org/r/20230623225529.34590-3-brgerst@gmail.com
This commit is contained in:
Brian Gerst 2023-06-23 18:55:29 -04:00 committed by Peter Zijlstra
parent 81f755d561
commit 3aec4ecb3d
4 changed files with 40 additions and 49 deletions
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30
arch/x86/entry/entry_32.S
View File

@ -727,36 +727,22 @@ SYM_CODE_END(__switch_to_asm)
* edi: kernel thread arg
*/
.pushsection .text, "ax"
SYM_CODE_START(ret_from_fork)
SYM_CODE_START(ret_from_fork_asm)
movl %esp, %edx /* regs */
/* return address for the stack unwinder */
pushl $.Lsyscall_32_done
FRAME_BEGIN
pushl %eax
call schedule_tail
/* prev already in EAX */
movl %ebx, %ecx /* fn */
pushl %edi /* fn_arg */
call ret_from_fork
addl $4, %esp
FRAME_END
testl %ebx, %ebx
jnz 1f /* kernel threads are uncommon */
2:
/* When we fork, we trace the syscall return in the child, too. */
leal 4(%esp), %eax
call syscall_exit_to_user_mode
RET
/* kernel thread */
1: movl %edi, %eax
CALL_NOSPEC ebx
/*
* A kernel thread is allowed to return here after successfully
* calling kernel_execve(). Exit to userspace to complete the execve()
* syscall.
*/
movl $0, PT_EAX(%esp)
jmp 2b
SYM_CODE_END(ret_from_fork)
SYM_CODE_END(ret_from_fork_asm)
.popsection
SYM_ENTRY(__begin_SYSENTER_singlestep_region, SYM_L_GLOBAL, SYM_A_NONE)

33
arch/x86/entry/entry_64.S
View File

@ -284,36 +284,19 @@ SYM_FUNC_END(__switch_to_asm)
* r12: kernel thread arg
*/
.pushsection .text, "ax"
__FUNC_ALIGN
SYM_CODE_START_NOALIGN(ret_from_fork)
UNWIND_HINT_END_OF_STACK
SYM_CODE_START(ret_from_fork_asm)
UNWIND_HINT_REGS
ANNOTATE_NOENDBR // copy_thread
CALL_DEPTH_ACCOUNT
movq %rax, %rdi
call schedule_tail /* rdi: 'prev' task parameter */
testq %rbx, %rbx /* from kernel_thread? */
jnz 1f /* kernel threads are uncommon */
movq %rax, %rdi /* prev */
movq %rsp, %rsi /* regs */
movq %rbx, %rdx /* fn */
movq %r12, %rcx /* fn_arg */
call ret_from_fork
2:
UNWIND_HINT_REGS
movq %rsp, %rdi
call syscall_exit_to_user_mode /* returns with IRQs disabled */
jmp swapgs_restore_regs_and_return_to_usermode
1:
/* kernel thread */
UNWIND_HINT_END_OF_STACK
movq %r12, %rdi
CALL_NOSPEC rbx
/*
* A kernel thread is allowed to return here after successfully
* calling kernel_execve(). Exit to userspace to complete the execve()
* syscall.
*/
movq $0, RAX(%rsp)
jmp 2b
SYM_CODE_END(ret_from_fork)
SYM_CODE_END(ret_from_fork_asm)
.popsection
.macro DEBUG_ENTRY_ASSERT_IRQS_OFF

4
arch/x86/include/asm/switch_to.h
View File

@ -12,7 +12,9 @@ struct task_struct *__switch_to_asm(struct task_struct *prev,
__visible struct task_struct *__switch_to(struct task_struct *prev,
struct task_struct *next);
asmlinkage void ret_from_fork(void);
asmlinkage void ret_from_fork_asm(void);
__visible void ret_from_fork(struct task_struct *prev, struct pt_regs *regs,
int (*fn)(void *), void *fn_arg);
/*
* This is the structure pointed to by thread.sp for an inactive task. The

22
arch/x86/kernel/process.c
View File

@ -28,6 +28,7 @@
#include <linux/static_call.h>
#include <trace/events/power.h>
#include <linux/hw_breakpoint.h>
#include <linux/entry-common.h>
#include <asm/cpu.h>
#include <asm/apic.h>
#include <linux/uaccess.h>
@ -134,6 +135,25 @@ static int set_new_tls(struct task_struct *p, unsigned long tls)
return do_set_thread_area_64(p, ARCH_SET_FS, tls);
}
__visible void ret_from_fork(struct task_struct *prev, struct pt_regs *regs,
int (*fn)(void *), void *fn_arg)
{
schedule_tail(prev);
/* Is this a kernel thread? */
if (unlikely(fn)) {
fn(fn_arg);
/*
* A kernel thread is allowed to return here after successfully
* calling kernel_execve(). Exit to userspace to complete the
* execve() syscall.
*/
regs->ax = 0;
}
syscall_exit_to_user_mode(regs);
}
int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
{
unsigned long clone_flags = args->flags;
@ -149,7 +169,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
frame = &fork_frame->frame;
frame->bp = encode_frame_pointer(childregs);
frame->ret_addr = (unsigned long) ret_from_fork;
frame->ret_addr = (unsigned long) ret_from_fork_asm;
p->thread.sp = (unsigned long) fork_frame;
p->thread.io_bitmap = NULL;
p->thread.iopl_warn = 0;