[PATCH] uml: fix hang in TT mode on fault (546fe1cb) · Commits · 戴 / test

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 <luothing@sina.com> Signed-off-by:

Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> Cc: Jeff Dike <jdike@addtoit.com> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

arch/um/kernel/trap_kern.c

+10 −1

Original line number	Diff line number	Diff line
		@@ -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");

		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)

arch/um/kernel/tt/uaccess_user.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -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)

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