Commit 20987de3 authored by Dave Martin's avatar Dave Martin Committed by Will Deacon
Browse files

arm64: signal: split frame link record from sigcontext structure 



In order to be able to increase the amount of the data currently
written to the __reserved[] array in the signal frame, it is
necessary to overwrite the locations currently occupied by the
{fp,lr} frame link record pushed at the top of the signal stack.

In order for this to work, this patch detaches the frame link
record from struct rt_sigframe and places it separately at the top
of the signal stack.  This will allow subsequent patches to insert
data between it and __reserved[].

This change relies on the non-ABI status of the placement of the
frame record with respect to struct sigframe: this status is
undocumented, but the placement is not declared or described in the
user headers, and known unwinder implementations (libgcc,
libunwind, gdb) appear not to rely on it.

Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 8f360948

arch/arm64/kernel/signal.c

+32 −18
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 


#include <linux/compat.h>

#include <linux/errno.h>

#include <linux/kernel.h>

#include <linux/signal.h>

#include <linux/personality.h>

#include <linux/freezer.h>
@@ -41,10 +42,18 @@ 
struct rt_sigframe {

	struct siginfo info;

	struct ucontext uc;

};



struct frame_record {

	u64 fp;

	u64 lr;

};



struct rt_sigframe_user_layout {

	struct rt_sigframe __user *sigframe;

	struct frame_record __user *next_frame;

};



static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)

{

	struct fpsimd_state *fpsimd = &current->thread.fpsimd_state;
@@ -162,16 +171,17 @@ badframe: 
	return 0;

}



static int setup_sigframe(struct rt_sigframe __user *sf,

static int setup_sigframe(struct rt_sigframe_user_layout *user,

			  struct pt_regs *regs, sigset_t *set)

{

	int i, err = 0;

	struct rt_sigframe __user *sf = user->sigframe;

	void *aux = sf->uc.uc_mcontext.__reserved;

	struct _aarch64_ctx *end;



	/* set up the stack frame for unwinding */

	__put_user_error(regs->regs[29], &sf->fp, err);

	__put_user_error(regs->regs[30], &sf->lr, err);

	__put_user_error(regs->regs[29], &user->next_frame->fp, err);

	__put_user_error(regs->regs[30], &user->next_frame->lr, err);



	for (i = 0; i < 31; i++)

		__put_user_error(regs->regs[i], &sf->uc.uc_mcontext.regs[i],
@@ -209,34 +219,36 @@ static int setup_sigframe(struct rt_sigframe __user *sf, 
	return err;

}



static struct rt_sigframe __user *get_sigframe(struct ksignal *ksig,

					       struct pt_regs *regs)

static int get_sigframe(struct rt_sigframe_user_layout *user,

			 struct ksignal *ksig, struct pt_regs *regs)

{

	unsigned long sp, sp_top;

	struct rt_sigframe __user *frame;



	sp = sp_top = sigsp(regs->sp, ksig);



	sp = (sp - sizeof(struct rt_sigframe)) & ~15;

	frame = (struct rt_sigframe __user *)sp;

	sp = round_down(sp - sizeof(struct frame_record), 16);

	user->next_frame = (struct frame_record __user *)sp;



	sp = round_down(sp - sizeof(struct rt_sigframe), 16);

	user->sigframe = (struct rt_sigframe __user *)sp;



	/*

	 * Check that we can actually write to the signal frame.

	 */

	if (!access_ok(VERIFY_WRITE, frame, sp_top - sp))

		frame = NULL;

	if (!access_ok(VERIFY_WRITE, user->sigframe, sp_top - sp))

		return -EFAULT;



	return frame;

	return 0;

}



static void setup_return(struct pt_regs *regs, struct k_sigaction *ka,

			 void __user *frame, int usig)

			 struct rt_sigframe_user_layout *user, int usig)

{

	__sigrestore_t sigtramp;



	regs->regs[0] = usig;

	regs->sp = (unsigned long)frame;

	regs->regs[29] = regs->sp + offsetof(struct rt_sigframe, fp);

	regs->sp = (unsigned long)user->sigframe;

	regs->regs[29] = (unsigned long)&user->next_frame->fp;

	regs->pc = (unsigned long)ka->sa.sa_handler;



	if (ka->sa.sa_flags & SA_RESTORER)
@@ -250,20 +262,22 @@ static void setup_return(struct pt_regs *regs, struct k_sigaction *ka, 
static int setup_rt_frame(int usig, struct ksignal *ksig, sigset_t *set,

			  struct pt_regs *regs)

{

	struct rt_sigframe_user_layout user;

	struct rt_sigframe __user *frame;

	int err = 0;



	frame = get_sigframe(ksig, regs);

	if (!frame)

	if (get_sigframe(&user, ksig, regs))

		return 1;



	frame = user.sigframe;



	__put_user_error(0, &frame->uc.uc_flags, err);

	__put_user_error(NULL, &frame->uc.uc_link, err);



	err |= __save_altstack(&frame->uc.uc_stack, regs->sp);

	err |= setup_sigframe(frame, regs, set);

	err |= setup_sigframe(&user, regs, set);

	if (err == 0) {

		setup_return(regs, &ksig->ka, frame, usig);

		setup_return(regs, &ksig->ka, &user, usig);

		if (ksig->ka.sa.sa_flags & SA_SIGINFO) {

			err |= copy_siginfo_to_user(&frame->info, &ksig->info);

			regs->regs[1] = (unsigned long)&frame->info;

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