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x86: Make IA32_EMULATION boot time configurable 

Distributions would like to reduce their attack surface as much as
possible but at the same time they'd want to retain flexibility to cater
to a variety of legacy software. This stems from the conjecture that
compat layer is likely rarely tested and could have latent security
bugs. Ideally distributions will set their default policy and also
give users the ability to override it as appropriate.

To enable this use case, introduce CONFIG_IA32_EMULATION_DEFAULT_DISABLED
compile time option, which controls whether 32bit processes/syscalls
should be allowed or not. This option is aimed mainly at distributions
to set their preferred default behavior in their kernels.

To allow users to override the distro's policy, introduce the 'ia32_emulation'
parameter which allows overriding CONFIG_IA32_EMULATION_DEFAULT_DISABLED
state at boot time.

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230623111409.3047467-7-nik.borisov@suse.com
This commit is contained in:
Nikolay Borisov 2023-06-23 14:14:09 +03:00 committed by Thomas Gleixner
parent 61382281e9
commit a11e097504
3 changed files with 23 additions and 1 deletions
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6
Documentation/admin-guide/kernel-parameters.txt
View File

@ -1893,6 +1893,12 @@
0 -- machine default
1 -- force brightness inversion
ia32_emulation= [X86-64]
Format: <bool>
When true, allows loading 32-bit programs and executing 32-bit
syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at
boot time. When false, unconditionally disables IA32 emulation.
icn= [HW,ISDN]
Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]

9
arch/x86/Kconfig
View File

@ -2954,6 +2954,15 @@ config IA32_EMULATION
64-bit kernel. You should likely turn this on, unless you're
100% sure that you don't have any 32-bit programs left.
config IA32_EMULATION_DEFAULT_DISABLED
bool "IA32 emulation disabled by default"
default n
depends on IA32_EMULATION
help
Make IA32 emulation disabled by default. This prevents loading 32-bit
processes and access to 32-bit syscalls. If unsure, leave it to its
default value.
config X86_X32_ABI
bool "x32 ABI for 64-bit mode"
depends on X86_64

9
arch/x86/entry/common.c
View File

@ -19,6 +19,7 @@
#include <linux/nospec.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <linux/init.h>
#ifdef CONFIG_XEN_PV
#include <xen/xen-ops.h>
@ -97,7 +98,13 @@ static __always_inline int syscall_32_enter(struct pt_regs *regs)
}
#ifdef CONFIG_IA32_EMULATION
bool __ia32_enabled __ro_after_init = true;
bool __ia32_enabled __ro_after_init = !IS_ENABLED(CONFIG_IA32_EMULATION_DEFAULT_DISABLED);
static int ia32_emulation_override_cmdline(char *arg)
{
return kstrtobool(arg, &__ia32_enabled);
}
early_param("ia32_emulation", ia32_emulation_override_cmdline);
#endif
/*