Messages in this thread | | | Date | Wed, 15 Jul 2020 12:51:23 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v3 1/3] kprobes: Add text_alloc() and text_free() |
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On Wed, Jul 15, 2020 at 10:49:33PM +0300, Mike Rapoport wrote: > On Wed, Jul 15, 2020 at 12:36:02PM -0700, Kees Cook wrote: > > On Wed, Jul 15, 2020 at 01:32:27AM +0300, Jarkko Sakkinen wrote: > > > Introduce new API for allocating space for code generaed at run-time > > > leveraging from module_alloc() and module_memfree() code. Use this to > > > perform memory allocations in the kprobes code in order to loose the > > > bound between kprobes and modules subsystem. > > > > > > Initially, use this API only with arch/x86 and define a new config > > > flag CONFIG_ARCH_HAS_TEXT_ALLOC to promote the availability of the > > > new API. > > > [...] > > > diff --git a/include/linux/text.h b/include/linux/text.h > > > new file mode 100644 > > > index 000000000000..a27d4a42ecda > > > --- /dev/null > > > +++ b/include/linux/text.h > > > @@ -0,0 +1,17 @@ > > > +/* SPDX-License-Identifier: GPL-2.0-only */ > > > + > > > +#ifndef _LINUX_TEXT_H > > > +#define _LINUX_TEXT_H > > > + > > > +/* > > > + * An allocator used for allocating modules, core sections and init sections. > > > + * Returns NULL on failure. > > > + */ > > > +void *text_alloc(unsigned long size); > > > + > > > +/* > > > + * Free memory returned from text_alloc(). > > > + */ > > > +void text_free(void *region); > > > + > > > +#endif /* _LINUX_TEXT_H */ > > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > > > index 2e97febeef77..fa7687eb0c0e 100644 > > > --- a/kernel/kprobes.c > > > +++ b/kernel/kprobes.c > > > @@ -35,6 +35,7 @@ > > > #include <linux/ftrace.h> > > > #include <linux/cpu.h> > > > #include <linux/jump_label.h> > > > +#include <linux/text.h> > > > > > > #include <asm/sections.h> > > > #include <asm/cacheflush.h> > > > @@ -111,12 +112,20 @@ enum kprobe_slot_state { > > > > > > void __weak *alloc_insn_page(void) > > > { > > > +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC > > > + return text_alloc(PAGE_SIZE); > > > +#else > > > return module_alloc(PAGE_SIZE); > > > +#endif > > > > This seems like it shouldn't be needed. I think text_alloc() should > > always be visible. In the ARCH_HAS... case it will call the arch > > implementation, and without it should just call module_alloc(): > > > > For example: > > void *text_alloc(unsigned long size) > > { > > #ifdef CONFIG_ARCH_HAS_TEXT_ALLOC > > return arch_text_alloc(size); > > #else > > return module_alloc(size); > > #endif > > } > > This inverts the dependcy chain, IMHO, module_alloc() is a special case > of text_alloc() and not vice versa.
Okay, sure. That's fine too. Whatever the case is, I want to make sure we keep the KASLR offset though. I don't think that should be unique to the modules logic.
-- Kees Cook
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