On Sun, Feb 21, 2021 at 12:25:53AM +0000, Sergei Trofimovich wrote: > 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). > > CC: Oleg Nesterov <o...@redhat.com> > CC: linux-i...@vger.kernel.org > CC: linux-kernel@vger.kernel.org > CC: Andrew Morton <a...@linux-foundation.org> > Reported-by: Dmitry V. Levin <l...@altlinux.org> > Bug: https://bugs.gentoo.org/769614 > Signed-off-by: Sergei Trofimovich <sly...@gentoo.org> > --- > arch/ia64/kernel/ptrace.c | 24 ++++++++++++++++++------ > 1 file changed, 18 insertions(+), 6 deletions(-) > > diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c > index c3490ee2daa5..e14f5653393a 100644 > --- a/arch/ia64/kernel/ptrace.c > +++ b/arch/ia64/kernel/ptrace.c > @@ -2013,27 +2013,39 @@ 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.
typo: epsinstruction > + * > + * For both cases argguments are reachable in cfm.sof - cfm.sol. typo: argguments > + * 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) { This stuff is too ia64 specific, so I cannot properly review this patch, but it definitely fixes ia64 PTRACE_GET_SYSCALL_INFO on entering syscall. -- ldv