linux-kernel - Re: [RFC v2 2/7] tables.h: add linker table support

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Date:	Wed, 24 Feb 2016 01:54:58 +0100
From:	"Luis R. Rodriguez" <mcgrof@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Michael Brown <mcb30@...e.org>,
	Juergen Gross <jgross@...e.com>,
	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	jbaron@...mai.com, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, David Miller <davem@...emloft.net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	andriy.shevchenko@...ux.intel.com,
	David Woodhouse <dwmw2@...radead.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	linux-security-module <linux-security-module@...r.kernel.org>
Subject: Re: [RFC v2 2/7] tables.h: add linker table support

On Tue, Feb 23, 2016 at 04:06:55PM -0800, H. Peter Anvin wrote:
> On 02/23/2016 03:36 PM, Luis R. Rodriguez wrote:
> > 
> >> 4. the only useful operator on a range is "is address X inside this
> >>    range"; this operator is likely *not* useful for a table, since
                                                     ^^^^^^^^^^^^
> >>    if you have to ever invoke it you are probably doing something very
> >>    wrong.
> > 
> > kprobe uses it :P
> > 
> 
> Could you explain how?

Sorry I misread this as "unless you are a table", kprobes has two
ranges, one is a table (blacklist) and the other just a range
(for kprobes); only kprobes uses "address inside this range",
as reflected below. So I agree with you.

index d10ab6b9b5e0..d816c659f358 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1328,8 +1328,7 @@ out:
 bool __weak arch_within_kprobe_blacklist(unsigned long addr)
 {
        /* The __kprobes marked functions and entry code must not be probed */
-       return addr >= (unsigned long)__kprobes_text_start &&
-              addr < (unsigned long)__kprobes_text_end;
+       return LINKTABLE_ADDR_WITHIN(kprobes, addr);
 }
 
 bool within_kprobe_blacklist(unsigned long addr)
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d10ab6b9b5e0..d816c659f358 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1328,8 +1328,7 @@ out:
 bool __weak arch_within_kprobe_blacklist(unsigned long addr)
 {
        /* The __kprobes marked functions and entry code must not be probed */
-       return addr >= (unsigned long)__kprobes_text_start &&
-              addr < (unsigned long)__kprobes_text_end;
+       return LINKTABLE_ADDR_WITHIN(kprobes, addr);
 }
 
What about rebranding general section primitives under section.h

#define DECLARE_SECTION_TEXT_TYPE(type, name)                              \       
         extern const type name[], name##__end[];

#define DECLARE_SECTION_TEXT(name)                              \       
	DECLARE_SECTION_TEXT_TYPE(char, name)

Then tables.h would use the TYPE version:

#define DECLARE_LINKTABLE_TEXT(type, name)                              \       
         DECLARE_SECTION_TEXT_TYPE(type, name)

Since I've been making _TEXT the implicit type for section names(SECTION_INIT
is .init.text) the above could just be DECLARE_SECTION_TYPE() and DECLARE_SECTION()
for text if we prefer.

  Luis