@@ -189,6 +189,7 @@ static void show_stacktrace(struct task_struct *task,
void show_stack(struct task_struct *task, unsigned long *sp)
{
struct pt_regs regs;
+ mm_segment_t old_fs = get_fs();
if (sp) {
regs.regs[29] = (unsigned long)sp;
regs.regs[31] = 0;
@@ -207,7 +208,13 @@ void show_stack(struct task_struct *task, unsigned long *sp)
prepare_frametrace(®s);
}
}
+ /*
+ * show_stack() deals exclusively with kernel mode, so be sure to access
+ * the stack in the kernel (not user) address space.
+ */
+ set_fs(KERNEL_DS);
show_stacktrace(task, ®s);
+ set_fs(old_fs);
}
static void show_code(unsigned int __user *pc)
This is a note to let you know that I have just added a patch titled MIPS: show_stack: Fix stack trace with EVA to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt17. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 4df98498550780b94a2164bdb81ea1c02caea928 Mon Sep 17 00:00:00 2001 From: James Hogan <james.hogan@imgtec.com> Date: Mon, 27 Jul 2015 13:50:22 +0100 Subject: MIPS: show_stack: Fix stack trace with EVA commit 1e77863a51698c4319587df34171bd823691a66a upstream. The show_stack() function deals exclusively with kernel contexts, but if it gets called in user context with EVA enabled, show_stacktrace() will attempt to access the stack using EVA accesses, which will either read other user mapped data, or more likely cause an exception which will be handled by __get_user(). This is easily reproduced using SysRq t to show all task states, which results in the following stack dump output: Stack : (Bad stack address) Fix by setting the current user access mode to kernel around the call to show_stacktrace(). This causes __get_user() to use normal loads to read the kernel stack. Now we get the correct output, like this: Stack : 00000000 80168960 00000000 004a0000 00000000 00000000 8060016c 1f3abd0c 1f172cd8 8056f09c 7ff1e450 8014fc3c 00000001 806dd0b0 0000001d 00000002 1f17c6a0 1f17c804 1f17c6a0 8066f6e0 00000000 0000000a 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 0110e800 1f3abd6c 1f17c6a0 ... Signed-off-by: James Hogan <james.hogan@imgtec.com> Cc: Markos Chandras <markos.chandras@imgtec.com> Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/10778/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- arch/mips/kernel/traps.c | 7 +++++++ 1 file changed, 7 insertions(+)