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SubjectRe: [PATCH -tip v4] [BUGFIX] kprobes/x86: Do not jump-optimize kprobes on irq entry code

* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Since the kernel segment registers are not prepared at the
> entry of irq-entry code, if a kprobe on such code is
> jump-optimized, accessing per-cpu variables may cause
> kernel panic.
> However, if the kprobe is not optimized, it kicks int3
> exception and set segment registers correctly.
>
> This checks probe-address and if it is in irq-entry code,
> it prohibits optimizing such kprobes. This means we can
> continuously probing such interrupt handlers by kprobes
> but it is not optimized anymore.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Reported-by: Francis Deslauriers <francis.deslauriers@efficios.com>
> Tested-by: Francis Deslauriers <francis.deslauriers@efficios.com>
> ---
> Changes in v4:
> - Fix to use CONFIG_OPTPROBES instead of CONFIG_KPROBES.
> ---
> arch/x86/kernel/kprobes/opt.c | 9 ++++++---
> include/asm-generic/vmlinux.lds.h | 6 ++++--
> include/linux/interrupt.h | 3 ++-
> 3 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
> index 69ea0bc..c26e7f9 100644
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -29,6 +29,7 @@
> #include <linux/kallsyms.h>
> #include <linux/ftrace.h>
> #include <linux/frame.h>
> +#include <linux/interrupt.h>
>
> #include <asm/text-patching.h>
> #include <asm/cacheflush.h>
> @@ -251,10 +252,12 @@ static int can_optimize(unsigned long paddr)
>
> /*
> * Do not optimize in the entry code due to the unstable
> - * stack handling.
> + * stack handling and registers setup.
> */
> - if ((paddr >= (unsigned long)__entry_text_start) &&
> - (paddr < (unsigned long)__entry_text_end))
> + if (((paddr >= (unsigned long)__entry_text_start) &&
> + (paddr < (unsigned long)__entry_text_end)) ||
> + ((paddr >= (unsigned long)__irqentry_text_start) &&
> + (paddr < (unsigned long)__irqentry_text_end)))
> return 0;
>
> /* Check there is enough space for a relative jump. */
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index da0be9a..3092a1f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -483,7 +483,8 @@
> *(.entry.text) \
> VMLINUX_SYMBOL(__entry_text_end) = .;
>
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || \
> + defined(CONFIG_OPTPROBES)
> #define IRQENTRY_TEXT \
> ALIGN_FUNCTION(); \
> VMLINUX_SYMBOL(__irqentry_text_start) = .; \
> @@ -493,7 +494,8 @@
> #define IRQENTRY_TEXT
> #endif
>
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || \
> + defined(CONFIG_OPTPROBES)
> #define SOFTIRQENTRY_TEXT \
> ALIGN_FUNCTION(); \
> VMLINUX_SYMBOL(__softirqentry_text_start) = .; \
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index a2fdddd..f95b046 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -726,7 +726,8 @@ extern int early_irq_init(void);
> extern int arch_probe_nr_irqs(void);
> extern int arch_early_irq_init(void);
>
> -#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)
> +#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN) || \
> + defined(CONFIG_OPTPROBES)

Please split the generic changes to asm-generic/vmlinux.lds.h and interrupt.h into
a separate patch, with its own changelog, because this is not a kprobes/x86 only
patch anymore.

Thanks,

Ingo

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