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SubjectRe: [ 06/37] x86-32: Fix invalid stack address while in softirq
On Fri, Nov 30, 2012 at 10:45:53AM -0800, Greg Kroah-Hartman wrote:
> 3.0-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Robert Richter <robert.richter@amd.com>
>
> commit 1022623842cb72ee4d0dbf02f6937f38c92c3f41 upstream.
>
> In 32 bit the stack address provided by kernel_stack_pointer() may
> point to an invalid range causing NULL pointer access or page faults
> while in NMI (see trace below). This happens if called in softirq
> context and if the stack is empty. The address at &regs->sp is then
> out of range.
>
> Fixing this by checking if regs and &regs->sp are in the same stack
> context. Otherwise return the previous stack pointer stored in struct
> thread_info. If that address is invalid too, return address of regs.
>
[...]

Hi, this makes build fail with oprofile on i386 on 3.0.54:
ERROR: "kernel_stack_pointer" [arch/x86/oprofile/oprofile.ko] undefined!

The following commit should address this failure:

commit cb57a2b4cff7edf2a4e32c0163200e9434807e0a
Author: H. Peter Anvin <hpa@linux.intel.com>
Date: Tue Nov 20 22:21:02 2012 -0800

x86-32: Export kernel_stack_pointer() for modules

Modules, in particular oprofile (and possibly other similar tools)
need kernel_stack_pointer(), so export it using EXPORT_SYMBOL_GPL().

>
> --- a/arch/x86/include/asm/ptrace.h
> +++ b/arch/x86/include/asm/ptrace.h
> @@ -187,21 +187,14 @@ static inline int v8086_mode(struct pt_r
> #endif
> }
>
> -/*
> - * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
> - * when it traps. The previous stack will be directly underneath the saved
> - * registers, and 'sp/ss' won't even have been saved. Thus the '&regs->sp'.
> - *
> - * This is valid only for kernel mode traps.
> - */
> -static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
> -{
> #ifdef CONFIG_X86_32
> - return (unsigned long)(&regs->sp);
> +extern unsigned long kernel_stack_pointer(struct pt_regs *regs);
> #else
> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
> +{
> return regs->sp;
> -#endif
> }
> +#endif
>
> #define GET_IP(regs) ((regs)->ip)
> #define GET_FP(regs) ((regs)->bp)
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -164,6 +164,34 @@ static inline bool invalid_selector(u16
>
> #define FLAG_MASK FLAG_MASK_32
>
> +/*
> + * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
> + * when it traps. The previous stack will be directly underneath the saved
> + * registers, and 'sp/ss' won't even have been saved. Thus the '&regs->sp'.
> + *
> + * Now, if the stack is empty, '&regs->sp' is out of range. In this
> + * case we try to take the previous stack. To always return a non-null
> + * stack pointer we fall back to regs as stack if no previous stack
> + * exists.
> + *
> + * This is valid only for kernel mode traps.
> + */
> +unsigned long kernel_stack_pointer(struct pt_regs *regs)
> +{
> + unsigned long context = (unsigned long)regs & ~(THREAD_SIZE - 1);
> + unsigned long sp = (unsigned long)&regs->sp;
> + struct thread_info *tinfo;
> +
> + if (context == (sp & ~(THREAD_SIZE - 1)))
> + return sp;
> +
> + tinfo = (struct thread_info *)context;
> + if (tinfo->previous_esp)
> + return tinfo->previous_esp;
> +
> + return (unsigned long)regs;
> +}
> +
> static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long regno)
> {
> BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);
>

--
[]'s
Herton


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