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authorRenzo Davoli <renzo@cs.unibo.it>2009-03-12 14:31:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-03-12 16:20:23 -0700
commit86d6f2bf61eb2a28fa63c0a19330d36226426477 (patch)
tree5eced3cf400712bd3b08038ee29feade9efb0466
parentf1c7404e37a8970bd58cc10a6d96534d42b9aac6 (diff)
downloadlinux-2.6.34-ux500-86d6f2bf61eb2a28fa63c0a19330d36226426477.tar.gz
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 <renzo@cs.unibo.it> Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com> Cc: Jeff Dike <jdike@addtoit.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/um/kernel/ptrace.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/um/kernel/ptrace.c b/arch/um/kernel/ptrace.c
index 15e8b7c4de1..8e3d69e4fcb 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. */