On Fri, Aug 28, 2020 at 01:03:00PM -0400, Rich Felker wrote: > On Fri, Aug 28, 2020 at 06:38:09PM +0200, John Paul Adrian Glaubitz wrote: > > Hi! > > > > On 8/28/20 6:30 PM, Rich Felker wrote: > > > I'm about to test a patch along these lines and will report what I > > > find. > > > > Let me know when you have something to test and I will test the patch as > > well, making sure we're not breaking seccomp again. > > If you have a seccomp test setup, please try the following patch. I'm > not sure if the end result is entirely correct, but I believe it's > at least much closer to correct than the code was before or after > adding SECCOMP_FILTER. > > > diff --git a/arch/sh/kernel/entry-common.S b/arch/sh/kernel/entry-common.S > index ad963104d22d..0560a8054215 100644 > --- a/arch/sh/kernel/entry-common.S > +++ b/arch/sh/kernel/entry-common.S > @@ -368,9 +368,6 @@ syscall_trace_entry: > mov.l 7f, r11 ! Call do_syscall_trace_enter which notifies > jsr @r11 ! superior (will chomp R[0-7]) > nop > - cmp/eq #-1, r0 > - bt syscall_exit > - mov.l r0, @(OFF_R0,r15) ! Save return value > ! Reload R0-R4 from kernel stack, where the > ! parent may have modified them using > ! ptrace(POKEUSR). (Note that R0-R2 are > @@ -382,7 +379,7 @@ syscall_trace_entry: > mov.l @(OFF_R5,r15), r5 > mov.l @(OFF_R6,r15), r6 > mov.l @(OFF_R7,r15), r7 ! arg3 > - mov.l @(OFF_R3,r15), r3 ! syscall_nr > + mov r0, r3 ! syscall_nr, possibly changed to -1 > ! > mov.l 6f, r10 ! Number of syscalls > cmp/hs r10, r3 > diff --git a/arch/sh/kernel/ptrace_32.c b/arch/sh/kernel/ptrace_32.c > index 25ccfbd02bfa..9e86cff041c7 100644 > --- a/arch/sh/kernel/ptrace_32.c > +++ b/arch/sh/kernel/ptrace_32.c > @@ -503,7 +503,7 @@ asmlinkage long do_syscall_trace_enter(struct pt_regs > *regs) > audit_syscall_entry(regs->regs[3], regs->regs[4], regs->regs[5], > regs->regs[6], regs->regs[7]); > > - return ret ?: regs->regs[0]; > + return ret ?: regs->regs[3]; > } > > asmlinkage void do_syscall_trace_leave(struct pt_regs *regs)
This restored my ability to use strace, and I've written and tested a minimal strace-like hack using SECCOMP_RET_USER_NOTIF that works as expected on both j2 and qemu-system-sh4, so I think the above is correct. Rich
