Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH v3 04/15] powerpc/kuap: Make disabling KUAP at boottime impossible except on book3s/64 | Date | Fri, 23 Jun 2023 19:05:15 +0200 |
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It is possible to disable KUAP at boottime with 'nosmap' parameter.
That is implemented with jump_label hence adds a 'nop' in front of each open/close of userspace access.
From a security point of view it makes sence to disallow disabling KUAP. And on processors like the 8xx where 'nop' is not seamless, it saves a few cycles.
In addition, objtool UACCESS validation cannot cope with that feature because it visits every static branches independentely and is not able to see that when a UACCESS enable is skipped, the matching UACCESS disable is skipped as well.
So make KUAP always active when selected in kernel config.
In the future it may be re-implemented by noping the instructions instead of using static branches.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> --- arch/powerpc/include/asm/kup.h | 4 +--- arch/powerpc/mm/book3s32/kuap.c | 15 ++++++--------- arch/powerpc/mm/init-common.c | 6 +++--- arch/powerpc/mm/nohash/kup.c | 8 +------- 4 files changed, 11 insertions(+), 22 deletions(-)
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h index 74b7f4cee2ed..a02340535efa 100644 --- a/arch/powerpc/include/asm/kup.h +++ b/arch/powerpc/include/asm/kup.h @@ -49,11 +49,9 @@ void setup_kuep(bool disabled); void setup_kuap(bool disabled); #ifndef kuap_is_disabled -extern struct static_key_false disable_kuap_key; - static __always_inline bool kuap_is_disabled(void) { - return static_branch_unlikely(&disable_kuap_key); + return false; } #endif #else diff --git a/arch/powerpc/mm/book3s32/kuap.c b/arch/powerpc/mm/book3s32/kuap.c index c5484729b595..639219d0a821 100644 --- a/arch/powerpc/mm/book3s32/kuap.c +++ b/arch/powerpc/mm/book3s32/kuap.c @@ -17,17 +17,14 @@ EXPORT_SYMBOL(kuap_unlock_all_ool); void setup_kuap(bool disabled) { - if (!disabled) { - kuap_lock_all_ool(); - init_mm.context.sr0 |= SR_KS; - current->thread.sr0 |= SR_KS; - } + WARN_ON(disabled); + + kuap_lock_all_ool(); + init_mm.context.sr0 |= SR_KS; + current->thread.sr0 |= SR_KS; if (smp_processor_id() != boot_cpuid) return; - if (disabled) - static_branch_enable(&disable_kuap_key); - else - pr_info("Activating Kernel Userspace Access Protection\n"); + pr_info("Activating Kernel Userspace Access Protection\n"); } diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c index 74e140b1efef..237086742ec7 100644 --- a/arch/powerpc/mm/init-common.c +++ b/arch/powerpc/mm/init-common.c @@ -32,9 +32,6 @@ EXPORT_SYMBOL_GPL(kernstart_virt_addr); bool disable_kuep = !IS_ENABLED(CONFIG_PPC_KUEP); bool disable_kuap = !IS_ENABLED(CONFIG_PPC_KUAP); -struct static_key_false disable_kuap_key; -EXPORT_SYMBOL(disable_kuap_key); - static int __init parse_nosmep(char *p) { if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64)) @@ -48,6 +45,9 @@ early_param("nosmep", parse_nosmep); static int __init parse_nosmap(char *p) { + if (!IS_ENABLED(CONFIG_PPC_BOOK3S_64)) + return 0; + disable_kuap = true; pr_warn("Disabling Kernel Userspace Access Protection\n"); return 0; diff --git a/arch/powerpc/mm/nohash/kup.c b/arch/powerpc/mm/nohash/kup.c index 4e22adfa2aa8..3bb79f89de06 100644 --- a/arch/powerpc/mm/nohash/kup.c +++ b/arch/powerpc/mm/nohash/kup.c @@ -15,13 +15,7 @@ #ifdef CONFIG_PPC_KUAP void setup_kuap(bool disabled) { - if (disabled) { - if (IS_ENABLED(CONFIG_40x)) - disable_kuep = true; - if (smp_processor_id() == boot_cpuid) - static_branch_enable(&disable_kuap_key); - return; - } + WARN_ON(disabled); pr_info("Activating Kernel Userspace Access Protection\n"); -- 2.40.1
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