Commit adf3709e authored Mar 12, 2021 by Sergei Trofimovich Committed by Greg Kroah-Hartman Mar 30, 2021

ia64: fix ia64_syscall_get_set_arguments() for break-based syscalls

[ Upstream commit 0ceb1ace4a2778e34a5414e5349712ae4dc41d85 ]

In https://bugs.gentoo.org/769614 Dmitry noticed that
`ptrace(PTRACE_GET_SYSCALL_INFO)` does not work for syscalls called via
glibc's syscall() wrapper.

ia64 has two ways to call syscalls from userspace: via `break` and via
`eps` instructions.

The difference is in stack layout:

1. `eps` creates simple stack frame: no locals, in{0..7} == out{0..8}
2. `break` uses userspace stack frame: may be locals (glibc provides
   one), in{0..7} == out{0..8}.

Both work fine in syscall handling cde itself.

But `ptrace(PTRACE_GET_SYSCALL_INFO)` uses unwind mechanism to
re-extract syscall arguments but it does not account for locals.

The change always skips locals registers. It should not change `eps`
path as kernel's handler already enforces locals=0 and fixes `break`.

Tested on v5.10 on rx3600 machine (ia64 9040 CPU).

Link: https://lkml.kernel.org/r/20210221002554.333076-1-slyfox@gentoo.org
Link: https://bugs.gentoo.org/769614


Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reported-by: Dmitry V. Levin <ldv@altlinux.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 4c083481

arch/ia64/kernel/ptrace.c

+18 −6

Original line number	Diff line number	Diff line
		@@ -2147,27 +2147,39 @@ static void syscall_get_set_args_cb(struct unw_frame_info info, void data)
		{
		struct syscall_get_set_args *args = data;
		struct pt_regs *pt = args->regs;
		unsigned long *krbs, cfm, ndirty;
		unsigned long *krbs, cfm, ndirty, nlocals, nouts;
		int i, count;

		if (unw_unwind_to_user(info) < 0)
		return;

		/*
		* We get here via a few paths:
		* - break instruction: cfm is shared with caller.
		* syscall args are in out= regs, locals are non-empty.
		* - epsinstruction: cfm is set by br.call
		* locals don't exist.
		*
		* For both cases argguments are reachable in cfm.sof - cfm.sol.
		* CFM: [ ... \| sor: 17..14 \| sol : 13..7 \| sof : 6..0 ]
		*/
		cfm = pt->cr_ifs;
		nlocals = (cfm >> 7) & 0x7f; /* aka sol */
		nouts = (cfm & 0x7f) - nlocals; /* aka sof - sol */
		krbs = (unsigned long *)info->task + IA64_RBS_OFFSET/8;
		ndirty = ia64_rse_num_regs(krbs, krbs + (pt->loadrs >> 19));

		count = 0;
		if (in_syscall(pt))
		count = min_t(int, args->n, cfm & 0x7f);
		count = min_t(int, args->n, nouts);

		/* Iterate over outs. */
		for (i = 0; i < count; i++) {
		int j = ndirty + nlocals + i + args->i;
		if (args->rw)
		*ia64_rse_skip_regs(krbs, ndirty + i + args->i) =
		args->args[i];
		*ia64_rse_skip_regs(krbs, j) = args->args[i];
		else
		args->args[i] = *ia64_rse_skip_regs(krbs,
		ndirty + i + args->i);
		args->args[i] = *ia64_rse_skip_regs(krbs, j);
		}

		if (!args->rw) {