Commit 8e411be6 authored Jun 22, 2020 by Will Deacon

arm64: compat: Always use sigpage for sigreturn trampoline



The 32-bit sigreturn trampoline in the compat sigpage matches the binary
representation of the arch/arm/ sigpage exactly. This is important for
debuggers (e.g. GDB) and unwinders (e.g. libunwind) since they rely
on matching the instruction sequence in order to identify that they are
unwinding through a signal. The same cannot be said for the sigreturn
trampoline in the compat vDSO, which defeats the unwinder heuristics and
instead attempts to use unwind directives for the unwinding. This is in
contrast to arch/arm/, which never uses the vDSO for sigreturn.

Ensure compatibility with arch/arm/ and existing unwinders by always
using the sigpage for the sigreturn trampoline, regardless of the
presence of the compat vDSO.

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

parent a39060b0

arch/arm64/kernel/signal32.c

+0 −25

Original line number	Diff line number	Diff line
		@@ -342,30 +342,6 @@ static void compat_setup_return(struct pt_regs regs, struct k_sigaction ka,
		retcode = ptr_to_compat(ka->sa.sa_restorer);
		} else {
		/* Set up sigreturn pointer */
		#ifdef CONFIG_COMPAT_VDSO
		void *vdso_base = current->mm->context.vdso;
		void *vdso_trampoline;

		if (ka->sa.sa_flags & SA_SIGINFO) {
		if (thumb) {
		vdso_trampoline = VDSO_SYMBOL(vdso_base,
		compat_rt_sigreturn_thumb);
		} else {
		vdso_trampoline = VDSO_SYMBOL(vdso_base,
		compat_rt_sigreturn_arm);
		}
		} else {
		if (thumb) {
		vdso_trampoline = VDSO_SYMBOL(vdso_base,
		compat_sigreturn_thumb);
		} else {
		vdso_trampoline = VDSO_SYMBOL(vdso_base,
		compat_sigreturn_arm);
		}
		}

		retcode = ptr_to_compat(vdso_trampoline) + thumb;
		#else
		unsigned int idx = thumb << 1;

		if (ka->sa.sa_flags & SA_SIGINFO)
		@@ -373,7 +349,6 @@ static void compat_setup_return(struct pt_regs regs, struct k_sigaction ka,

		retcode = (unsigned long)current->mm->context.sigpage +
		(idx << 2) + thumb;
		#endif
		}

		regs->regs[0] = usig;

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