From 546fe1cbf91d4d62e3849517c31a2327c992e5c5 Mon Sep 17 00:00:00 2001 From: Paolo 'Blaisorblade' Giarrusso Date: Thu, 22 Sep 2005 21:44:16 -0700 Subject: [PATCH] [PATCH] uml: fix hang in TT mode on fault The current code doesn't handle well general protection faults on the host - it thinks that cr2 is always the address of a page fault. While actually, on general protection faults, that address is not accessible, so we'd better assume we couldn't satisfy the fault. Currently instead we think we've fixed it, so we go back, retry the instruction and fault again endlessly. This leads to the kernel hanging when doing copy_from_user(dest, -1, ...) in TT mode, since reading *(-1) causes a GFP, and we don't support kernel preemption. Thanks to Luo Xin for testing UML with LTP and reporting the failures he got. Cc: Luo Xin Signed-off-by: Paolo 'Blaisorblade' Giarrusso Cc: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/kernel/trap_kern.c | 11 ++++++++++- arch/um/kernel/tt/uaccess_user.c | 11 +++++++++-- 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/arch/um/kernel/trap_kern.c b/arch/um/kernel/trap_kern.c index 87cc6fd76ced..90690b9b1f30 100644 --- a/arch/um/kernel/trap_kern.c +++ b/arch/um/kernel/trap_kern.c @@ -18,6 +18,7 @@ #include "asm/a.out.h" #include "asm/current.h" #include "asm/irq.h" +#include "sysdep/sigcontext.h" #include "user_util.h" #include "kern_util.h" #include "kern.h" @@ -125,7 +126,15 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user, void *sc) } else if(current->mm == NULL) panic("Segfault with no mm"); - err = handle_page_fault(address, ip, is_write, is_user, &si.si_code); + + if (SEGV_IS_FIXABLE(&fi)) + err = handle_page_fault(address, ip, is_write, is_user, &si.si_code); + else { + err = -EFAULT; + /* A thread accessed NULL, we get a fault, but CR2 is invalid. + * This code is used in __do_copy_from_user() of TT mode. */ + address = 0; + } catcher = current->thread.fault_catcher; if(!err) diff --git a/arch/um/kernel/tt/uaccess_user.c b/arch/um/kernel/tt/uaccess_user.c index f01475512ecb..8c220f054b61 100644 --- a/arch/um/kernel/tt/uaccess_user.c +++ b/arch/um/kernel/tt/uaccess_user.c @@ -22,8 +22,15 @@ int __do_copy_from_user(void *to, const void *from, int n, __do_copy, &faulted); TASK_REGS(get_current())->tt = save; - if(!faulted) return(0); - else return(n - (fault - (unsigned long) from)); + if(!faulted) + return 0; + else if (fault) + return n - (fault - (unsigned long) from); + else + /* In case of a general protection fault, we don't have the + * fault address, so NULL is used instead. Pretend we didn't + * copy anything. */ + return n; } static void __do_strncpy(void *dst, const void *src, int count) -- 2.20.1