From: Benjamin Gray <bgray@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org
Cc: ajd@linux.ibm.com, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org, cmr@bluescreens.de,
Benjamin Gray <bgray@linux.ibm.com>
Subject: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override
Date: Mon, 28 Nov 2022 13:44:52 +1100 [thread overview]
Message-ID: <20221128024458.46121-8-bgray@linux.ibm.com> (raw)
In-Reply-To: <20221128024458.46121-1-bgray@linux.ibm.com>
The DEXCR Speculative Branch Hint Enable (SBHE) aspect controls whether
the hints provided by BO field of Branch instructions are obeyed during
speculative execution.
SBHE behaviour per ISA 3.1B:
0: The hints provided by BO field of Branch instructions may be
ignored during speculative execution
1: The hints provided by BO field of Branch instructions are obeyed
during speculative execution
Add a sysctl entry to allow changing this aspect globally in the system
at runtime:
/proc/sys/kernel/speculative_branch_hint_enable
Three values are supported:
-1: Disable DEXCR SBHE sysctl override
0: Override and set DEXCR[SBHE] aspect to 0
1: Override and set DEXCR[SBHE] aspect to 1
Internally, introduces a mechanism to apply arbitrary system wide
overrides on top of the prctl() config.
Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
---
arch/powerpc/kernel/dexcr.c | 125 ++++++++++++++++++++++++++++++++++++
1 file changed, 125 insertions(+)
diff --git a/arch/powerpc/kernel/dexcr.c b/arch/powerpc/kernel/dexcr.c
index 9290beed722a..8239bcc92026 100644
--- a/arch/powerpc/kernel/dexcr.c
+++ b/arch/powerpc/kernel/dexcr.c
@@ -1,8 +1,11 @@
#include <linux/cache.h>
#include <linux/capability.h>
+#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/prctl.h>
#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/sysctl.h>
#include <asm/cpu_has_feature.h>
#include <asm/cputable.h>
@@ -18,6 +21,58 @@
#define DEXCR_PRCTL_EDITABLE (DEXCR_PRO_SBHE | DEXCR_PRO_IBRTPD | \
DEXCR_PRO_SRAPD | DEXCR_PRO_NPHIE)
+/*
+ * Lock to protect system DEXCR override from concurrent updates.
+ * RCU semantics: writers take lock, readers are unlocked.
+ * Writers ensure the memory update is atomic, readers read
+ * atomically.
+ */
+static DEFINE_SPINLOCK(dexcr_sys_enforced_write_lock);
+
+struct mask_override {
+ union {
+ struct {
+ unsigned int mask;
+ unsigned int override;
+ };
+
+ /* Raw access for atomic read/write */
+ unsigned long all;
+ };
+};
+
+static struct mask_override dexcr_sys_enforced;
+
+static int spec_branch_hint_enable = -1;
+
+static void update_userspace_system_dexcr(unsigned int pro_mask, int value)
+{
+ struct mask_override update = { .all = 0 };
+
+ switch (value) {
+ case -1: /* Clear the mask bit, clear the override bit */
+ break;
+ case 0: /* Set the mask bit, clear the override bit */
+ update.mask |= pro_mask;
+ break;
+ case 1: /* Set the mask bit, set the override bit */
+ update.mask |= pro_mask;
+ update.override |= pro_mask;
+ break;
+ }
+
+ spin_lock(&dexcr_sys_enforced_write_lock);
+
+ /* Use the existing values for the non-updated bits */
+ update.mask |= dexcr_sys_enforced.mask & ~pro_mask;
+ update.override |= dexcr_sys_enforced.override & ~pro_mask;
+
+ /* Atomically update system enforced aspects */
+ WRITE_ONCE(dexcr_sys_enforced.all, update.all);
+
+ spin_unlock(&dexcr_sys_enforced_write_lock);
+}
+
static int __init dexcr_init(void)
{
if (!early_cpu_has_feature(CPU_FTR_ARCH_31))
@@ -25,6 +80,9 @@ static int __init dexcr_init(void)
mtspr(SPRN_DEXCR, DEFAULT_DEXCR);
+ if (early_cpu_has_feature(CPU_FTR_DEXCR_SBHE))
+ update_userspace_system_dexcr(DEXCR_PRO_SBHE, spec_branch_hint_enable);
+
return 0;
}
early_initcall(dexcr_init);
@@ -52,9 +110,15 @@ unsigned long get_thread_dexcr(struct thread_struct const *t)
{
unsigned long dexcr = DEFAULT_DEXCR;
+ /* Atomically read enforced mask & override */
+ struct mask_override enforced = READ_ONCE(dexcr_sys_enforced);
+
/* Apply prctl overrides */
dexcr = (dexcr & ~t->dexcr_mask) | t->dexcr_override;
+ /* Apply system overrides */
+ dexcr = (dexcr & ~enforced.mask) | enforced.override;
+
return dexcr;
}
@@ -176,3 +240,64 @@ int dexcr_prctl_set(struct task_struct *task, unsigned long which, unsigned long
return 0;
}
+
+#ifdef CONFIG_SYSCTL
+
+static const int min_sysctl_val = -1;
+
+static int sysctl_dexcr_sbhe_handler(struct ctl_table *table, int write,
+ void *buf, size_t *lenp, loff_t *ppos)
+{
+ int err;
+ int prev = spec_branch_hint_enable;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (!cpu_has_feature(CPU_FTR_DEXCR_SBHE))
+ return -ENODEV;
+
+ err = proc_dointvec_minmax(table, write, buf, lenp, ppos);
+ if (err)
+ return err;
+
+ if (prev != spec_branch_hint_enable && write) {
+ update_userspace_system_dexcr(DEXCR_PRO_SBHE, spec_branch_hint_enable);
+ cpus_read_lock();
+ on_each_cpu(update_dexcr_on_cpu, NULL, 1);
+ cpus_read_unlock();
+ }
+
+ return 0;
+}
+
+static struct ctl_table dexcr_sbhe_ctl_table[] = {
+ {
+ .procname = "speculative_branch_hint_enable",
+ .data = &spec_branch_hint_enable,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = sysctl_dexcr_sbhe_handler,
+ .extra1 = (void *)&min_sysctl_val,
+ .extra2 = SYSCTL_ONE,
+ },
+ {}
+};
+
+static struct ctl_table dexcr_sbhe_ctl_root[] = {
+ {
+ .procname = "kernel",
+ .mode = 0555,
+ .child = dexcr_sbhe_ctl_table,
+ },
+ {}
+};
+
+static int __init register_dexcr_aspects_sysctl(void)
+{
+ register_sysctl_table(dexcr_sbhe_ctl_root);
+ return 0;
+}
+device_initcall(register_dexcr_aspects_sysctl);
+
+#endif /* CONFIG_SYSCTL */
--
2.38.1
next prev parent reply other threads:[~2022-11-28 2:58 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-28 2:44 [RFC PATCH 00/13] Add DEXCR support Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 01/13] powerpc/book3s: Add missing <linux/sched.h> include Benjamin Gray
2023-03-07 4:28 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 02/13] powerpc: Add initial Dynamic Execution Control Register (DEXCR) support Benjamin Gray
2023-03-07 4:45 ` Nicholas Piggin
2023-03-09 23:46 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 03/13] powerpc/dexcr: Handle hashchk exception Benjamin Gray
2022-11-29 10:39 ` Nicholas Piggin
2022-11-29 22:04 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 04/13] powerpc/dexcr: Support userspace ROP protection Benjamin Gray
2023-03-07 5:05 ` Nicholas Piggin
2023-03-07 5:37 ` Benjamin Gray
2023-03-21 4:51 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 05/13] prctl: Define PowerPC DEXCR interface Benjamin Gray
2023-03-07 5:07 ` Nicholas Piggin
2022-11-28 2:44 ` [RFC PATCH 06/13] powerpc/dexcr: Add prctl implementation Benjamin Gray
2023-03-07 5:12 ` Nicholas Piggin
2022-11-28 2:44 ` Benjamin Gray [this message]
2023-03-07 5:30 ` [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override Nicholas Piggin
2023-03-07 5:58 ` Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 08/13] powerpc/dexcr: Add enforced userspace ROP protection config Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 09/13] selftests/powerpc: Add more utility macros Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 10/13] selftests/powerpc: Add hashst/hashchk test Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 11/13] selftests/powerpc: Add DEXCR prctl, sysctl interface test Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 12/13] selftests/powerpc: Add DEXCR status utility lsdexcr Benjamin Gray
2022-11-28 2:44 ` [RFC PATCH 13/13] Documentation: Document PowerPC kernel DEXCR interface Benjamin Gray
2023-03-07 5:40 ` Nicholas Piggin
2023-03-07 5:52 ` Benjamin Gray
2022-11-28 4:05 ` [RFC PATCH 00/13] Add DEXCR support Russell Currey
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20221128024458.46121-8-bgray@linux.ibm.com \
--to=bgray@linux.ibm.com \
--cc=ajd@linux.ibm.com \
--cc=cmr@bluescreens.de \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).