Hello,
On Wed, Aug 13, 2014 at 06:06:29PM +0100, Kees Cook wrote:
> From: Rabin Vincent <rabin@xxxxxx>
>
> Use fixmaps for text patching when the kernel text is read-only,
> inspired by x86. This makes jump labels and kprobes work with the
> currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming
> CONFIG_DEBUG_RODATA options.
>
> Signed-off-by: Rabin Vincent <rabin@xxxxxx>
> [kees: fixed up for merge with "arm: use generic fixmap.h"]
> [kees: added parse acquire/release annotations to pass C=1 builds]
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
[...]
> diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
> index 07314af47733..a1dce690446a 100644
> --- a/arch/arm/kernel/patch.c
> +++ b/arch/arm/kernel/patch.c
> @@ -1,8 +1,11 @@
> #include <linux/kernel.h>
> +#include <linux/spinlock.h>
> #include <linux/kprobes.h>
> +#include <linux/mm.h>
> #include <linux/stop_machine.h>
>
> #include <asm/cacheflush.h>
> +#include <asm/fixmap.h>
> #include <asm/smp_plat.h>
> #include <asm/opcodes.h>
>
> @@ -13,21 +16,77 @@ struct patch {
> unsigned int insn;
> };
>
> -void __kprobes __patch_text(void *addr, unsigned int insn)
> +static DEFINE_SPINLOCK(patch_lock);
> +
> +static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
> + __acquires(&patch_lock)
> +{
> + unsigned int uintaddr = (uintptr_t) addr;
> + bool module = !core_kernel_text(uintaddr);
> + struct page *page;
> +
> + if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
> + page = vmalloc_to_page(addr);
> + else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
> + page = virt_to_page(addr);
> + else
> + return addr;
> +
> + if (flags)
> + spin_lock_irqsave(&patch_lock, *flags);
> + else
> + __acquire(&patch_lock);
I don't understand the locking here. Why is it conditional, why do we need
to disable interrupts, and are you just racing against yourself?
> + set_fixmap(fixmap, page_to_phys(page));
set_fixmap does TLB invalidation, right? I think that means it can block on
11MPCore and A15 w/ the TLBI erratum, so it's not safe to call this with
interrupts disabled anyway.
Will
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