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UML - arch_prctl should set thread fs

PATCH New Jeff Dike 1 participant 1 message Mar 7, 2007 User-mode Linux (UML)

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Jeff Dike

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PATCH 1/1 UML - arch_prctl should set thread fs

[ Andrew, this is definite 2.6.21 material ]

In my previous x86_64 thread fix, I forgot to initialize thread.arch.fs in arch_prctl. A process calling arch_prctl to set %fs would lose it on the next context switch.

It also turns out that you can switch to a process which is in the process of exiting and which has lost its mm. In this case, it's worse than useless to try to call arch_prctl on the host process.

Signed-off-by Jeff Dike <[email protected]>

--

 arch/um/sys-x86_64/syscalls.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
arch/um/sys-x86_64/syscalls.c +4 -2
Index: linux-2.6.18-mm/arch/um/sys-x86_64/syscalls.c
===================================================================
@@ -103,6 +103,9 @@ long arch_prctl_skas(struct task_struct 
 
         switch(code){
 	case ARCH_SET_FS:
+		current->thread.arch.fs = (unsigned long) ptr;
+		save_registers(pid, &current->thread.regs.regs);
+		break;
 	case ARCH_SET_GS:
                 save_registers(pid, &current->thread.regs.regs);
 		break;

@@ -140,9 +143,8 @@ long sys_clone(unsigned long clone_flags
 
 void arch_switch_to_skas(struct task_struct *from, struct task_struct *to)
 {
-        if(to->thread.arch.fs == 0)
+        if((to->thread.arch.fs == 0) || (to->mm == NULL))
                 return;
 
         arch_prctl_skas(to, ARCH_SET_FS, (void __user *) to->thread.arch.fs);
 }
-