From 86d6f2bf61eb2a28fa63c0a19330d36226426477 Mon Sep 17 00:00:00 2001 From: Renzo Davoli Date: Thu, 12 Mar 2009 14:31:23 -0700 Subject: [PATCH] UML on UML fixed: it did not start It is currently impossible to run a user-mode linux machine inside another user-mode linux (UML on UML). It breaks after a few instructions. When it tries to check whether SYSEMU is installed (the inner) UML receives an inconsistent result (from the outer UML). This is the output of a broken attempt: $ ./linux mem=256m ubd0=cow Locating the bottom of the address space ... 0x0 Locating the top of the address space ... 0xc0000000 Core dump limits : soft - 0 hard - NONE Checking that ptrace can change system call numbers...OK Checking ptrace new tags for syscall emulation...unsupported Checking syscall emulation patch for ptrace...check_sysemu : expected SIGTRAP, got status = 256 $ The problem is the following: PTRACE_SYSCALL/SINGLESTEP is currently managed inside arch_ptrace for ARCH=um. PTRACE_SYSEMU/SUSEMU_SINGLESTEP is not captured in arch_ptrace's switch, therefore it is erroneously passed back to ptrace_request (in kernel/ptrace). This simple patch simply forces ptrace to return an error on PTRACE_SYSEMU/SUSEMU_SINGLESTEP as it is unsupported on ARCH=um, and fixes the problem. [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Renzo Davoli Reviewed-by: WANG Cong Cc: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/kernel/ptrace.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/um/kernel/ptrace.c b/arch/um/kernel/ptrace.c index 15e8b7c4de13..8e3d69e4fcb5 100644 --- a/arch/um/kernel/ptrace.c +++ b/arch/um/kernel/ptrace.c @@ -64,6 +64,11 @@ long arch_ptrace(struct task_struct *child, long request, long addr, long data) ret = poke_user(child, addr, data); break; + case PTRACE_SYSEMU: + case PTRACE_SYSEMU_SINGLESTEP: + ret = -EIO; + break; + /* continue and stop at next (return from) syscall */ case PTRACE_SYSCALL: /* restart after signal. */ -- 2.20.1