[2.6 patch] let CONFIG_SECCOMP default to n

Adrian Bunk
2006-06-29T19:23:31Z

From: Ingo Molnar <mingo@elte.hu>

I was profiling the scheduler on x86 and noticed some overhead related
to SECCOMP, and indeed, SECCOMP runs disable_tsc() at _every_
context-switch:

if (unlikely(prev->io_bitmap_ptr || next->io_bitmap_ptr))
handle_io_bitmap(next, tss);

disable_tsc(prev_p, next_p);

return prev_p;

these are a couple of instructions in the hottest scheduler codepath!

x86_64 already removed disable_tsc() from switch_to(), but i think the
right solution is to turn SECCOMP off by default.

besides the runtime overhead, there are a couple of other reasons as
well why this should be done:

- CONFIG_SECCOMP=y adds 836 bytes of bloat to the kernel:

text data bss dec hex filename
4185360 867112 391012 5443484 530f9c vmlinux-noseccomp
4185992 867316 391012 5444320 5312e0 vmlinux-seccomp

- virtually nobody seems to be using it (but cpushare.com, which seems
pretty inactive)

- users/distributions can still turn it on if they want it

- http://www.cpushare.com/legal seems to suggest that it is pursuing a
software patent to utilize the seccomp concept in a distributed
environment, and seems to give a promise that 'end users' will not be
affected by that patent. How about non-end-users [i.e. server-side]?
Has the Linux kernel become a vehicle for a propriety server-side
feature, with every Linux user paying the price of it?

so the patch below just does the minimal common-sense change: turn it
off by default.

Adrian Bunk:
I've removed the superfluous "default n"'s the original patch introduced.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

----

This patch was already sent on:
- 26 Jun 2006
- 27 Apr 2006
- 19 Apr 2006
- 11 Apr 2006
- 10 Mar 2006
- 29 Jan 2006
- 21 Jan 2006

This patch was sent by Ingo Molnar on:
- 9 Jan 2006

Index: linux/arch/i386/Kconfig
===================================================================
--- linux.orig/arch/i386/Kconfig
+++ linux/arch/i386/Kconfig
@@ -637,7 +637,6 @@ config REGPARM
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/mips/Kconfig
===================================================================
--- linux.orig/arch/mips/Kconfig
+++ linux/arch/mips/Kconfig
@@ -1787,7 +1787,6 @@ config BINFMT_ELF32
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS && BROKEN
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/powerpc/Kconfig
===================================================================
--- linux.orig/arch/powerpc/Kconfig
+++ linux/arch/powerpc/Kconfig
@@ -666,7 +666,6 @@ endif
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/ppc/Kconfig
===================================================================
--- linux.orig/arch/ppc/Kconfig
+++ linux/arch/ppc/Kconfig
@@ -1127,7 +1127,6 @@ endif
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/sparc64/Kconfig
===================================================================
--- linux.orig/arch/sparc64/Kconfig
+++ linux/arch/sparc64/Kconfig
@@ -64,7 +64,6 @@ endchoice
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their
Index: linux/arch/x86_64/Kconfig
===================================================================
--- linux.orig/arch/x86_64/Kconfig
+++ linux/arch/x86_64/Kconfig
@@ -466,7 +466,6 @@ config PHYSICAL_START
config SECCOMP
bool "Enable seccomp to safely compute untrusted bytecode"
depends on PROC_FS
- default y
help
This kernel feature is useful for number crunching applications
that may need to compute untrusted bytecode during their