From 20987de3c2c45c314e0386f724aa85f55d984ef2 Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Thu, 15 Jun 2017 15:03:38 +0100 Subject: [PATCH] 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: Catalin Marinas Signed-off-by: Dave Martin Signed-off-by: Will Deacon --- arch/arm64/kernel/signal.c | 50 ++++++++++++++++++++++++-------------- 1 file changed, 32 insertions(+), 18 deletions(-) diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c index c7b6de62f9d3..1e5ed3be78ed 100644 --- a/arch/arm64/kernel/signal.c +++ b/arch/arm64/kernel/signal.c @@ -19,6 +19,7 @@ #include #include +#include #include #include #include @@ -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 = ¤t->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; -- 2.39.2