kstack_offset was previously maintained per-cpu, but this caused a
couple of issues. So let's instead make it per-task.
Issue 1: add_random_kstack_offset() and choose_random_kstack_offset()
expected and required to be called with interrupts and preemption
disabled so that it could manipulate per-cpu state. But arm64, loongarch
and risc-v are calling them with interrupts and preemption enabled. I
don't _think_ this causes any functional issues, but it's certainly
unexpected and could lead to manipulating the wrong cpu's state, which
could cause a minor performance degradation due to bouncing the cache
lines. By maintaining the state per-task those functions can safely be
called in preemptible context.
Issue 2: add_random_kstack_offset() is called before executing the
syscall and expands the stack using a previously chosen rnadom offset.
choose_random_kstack_offset() is called after executing the syscall and
chooses and stores a new random offset for the next syscall. With
per-cpu storage for this offset, an attacker could force cpu migration
during the execution of the syscall and prevent the offset from being
updated for the original cpu such that it is predictable for the next
syscall on that cpu. By maintaining the state per-task, this problem
goes away because the per-task random offset is updated after the
syscall regardless of which cpu it is executing on.
Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall")
Closes: https://lore.kernel.org/all/dd8c37bc-795f-4c7a-9086-69e584d8ab24@arm.com/
Cc: stable(a)vger.kernel.org
Signed-off-by: Ryan Roberts <ryan.roberts(a)arm.com>
---
include/linux/randomize_kstack.h | 26 +++++++++++++++-----------
include/linux/sched.h | 4 ++++
init/main.c | 1 -
kernel/fork.c | 2 ++
4 files changed, 21 insertions(+), 12 deletions(-)
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h
index 1d982dbdd0d0..5d3916ca747c 100644
--- a/include/linux/randomize_kstack.h
+++ b/include/linux/randomize_kstack.h
@@ -9,7 +9,6 @@
DECLARE_STATIC_KEY_MAYBE(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT,
randomize_kstack_offset);
-DECLARE_PER_CPU(u32, kstack_offset);
/*
* Do not use this anywhere else in the kernel. This is used here because
@@ -50,15 +49,14 @@ DECLARE_PER_CPU(u32, kstack_offset);
* add_random_kstack_offset - Increase stack utilization by previously
* chosen random offset
*
- * This should be used in the syscall entry path when interrupts and
- * preempt are disabled, and after user registers have been stored to
- * the stack. For testing the resulting entropy, please see:
- * tools/testing/selftests/lkdtm/stack-entropy.sh
+ * This should be used in the syscall entry path after user registers have been
+ * stored to the stack. Preemption may be enabled. For testing the resulting
+ * entropy, please see: tools/testing/selftests/lkdtm/stack-entropy.sh
*/
#define add_random_kstack_offset() do { \
if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
&randomize_kstack_offset)) { \
- u32 offset = raw_cpu_read(kstack_offset); \
+ u32 offset = current->kstack_offset; \
u8 *ptr = __kstack_alloca(KSTACK_OFFSET_MAX(offset)); \
/* Keep allocation even after "ptr" loses scope. */ \
asm volatile("" :: "r"(ptr) : "memory"); \
@@ -69,9 +67,9 @@ DECLARE_PER_CPU(u32, kstack_offset);
* choose_random_kstack_offset - Choose the random offset for the next
* add_random_kstack_offset()
*
- * This should only be used during syscall exit when interrupts and
- * preempt are disabled. This position in the syscall flow is done to
- * frustrate attacks from userspace attempting to learn the next offset:
+ * This should only be used during syscall exit. Preemption may be enabled. This
+ * position in the syscall flow is done to frustrate attacks from userspace
+ * attempting to learn the next offset:
* - Maximize the timing uncertainty visible from userspace: if the
* offset is chosen at syscall entry, userspace has much more control
* over the timing between choosing offsets. "How long will we be in
@@ -85,14 +83,20 @@ DECLARE_PER_CPU(u32, kstack_offset);
#define choose_random_kstack_offset(rand) do { \
if (static_branch_maybe(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT, \
&randomize_kstack_offset)) { \
- u32 offset = raw_cpu_read(kstack_offset); \
+ u32 offset = current->kstack_offset; \
offset = ror32(offset, 5) ^ (rand); \
- raw_cpu_write(kstack_offset, offset); \
+ current->kstack_offset = offset; \
} \
} while (0)
+
+static inline void random_kstack_task_init(struct task_struct *tsk)
+{
+ tsk->kstack_offset = 0;
+}
#else /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
#define add_random_kstack_offset() do { } while (0)
#define choose_random_kstack_offset(rand) do { } while (0)
+#define random_kstack_task_init(tsk) do { } while (0)
#endif /* CONFIG_RANDOMIZE_KSTACK_OFFSET */
#endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d395f2810fac..9e0080ed1484 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1591,6 +1591,10 @@ struct task_struct {
unsigned long prev_lowest_stack;
#endif
+#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
+ u32 kstack_offset;
+#endif
+
#ifdef CONFIG_X86_MCE
void __user *mce_vaddr;
__u64 mce_kflags;
diff --git a/init/main.c b/init/main.c
index b84818ad9685..27fcbbde933e 100644
--- a/init/main.c
+++ b/init/main.c
@@ -830,7 +830,6 @@ static inline void initcall_debug_enable(void)
#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET
DEFINE_STATIC_KEY_MAYBE_RO(CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT,
randomize_kstack_offset);
-DEFINE_PER_CPU(u32, kstack_offset);
static int __init early_randomize_kstack_offset(char *buf)
{
diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8e..b061e1edbc43 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -95,6 +95,7 @@
#include <linux/thread_info.h>
#include <linux/kstack_erase.h>
#include <linux/kasan.h>
+#include <linux/randomize_kstack.h>
#include <linux/scs.h>
#include <linux/io_uring.h>
#include <linux/bpf.h>
@@ -2231,6 +2232,7 @@ __latent_entropy struct task_struct *copy_process(
if (retval)
goto bad_fork_cleanup_io;
+ random_kstack_task_init(p);
stackleak_task_init(p);
if (pid != &init_struct_pid) {
--
2.43.0
Commit 7f9ab862e05c ("leds: spi-byte: Call of_node_put() on error path")
was merged in 6.11 and then backported to stable trees through 5.10. It
relocates the line that initializes the variable 'child' to a later
point in spi_byte_probe().
Versions < 6.9 do not have commit ccc35ff2fd29 ("leds: spi-byte: Use
devm_led_classdev_register_ext()"), which removes a line that reads a
property from 'child' before its new initialization point. Consequently,
spi_byte_probe() reads from an uninitialized device node in stable
kernels 6.6-5.10.
Initialize 'child' before it is first accessed.
Fixes: 7f9ab862e05c ("leds: spi-byte: Call of_node_put() on error path")
Signed-off-by: Tiffany Yang <ynaffit(a)google.com>
---
As an alternative to moving the initialization of 'child' up,
Fedor Pchelkin proposed [1] backporting the change that removes the
intermediate access.
[1] https://lore.kernel.org/stable/20241029204128.527033-1-pchelkin@ispras.ru/
---
drivers/leds/leds-spi-byte.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/leds/leds-spi-byte.c b/drivers/leds/leds-spi-byte.c
index afe9bff7c7c1..4520df1e2341 100644
--- a/drivers/leds/leds-spi-byte.c
+++ b/drivers/leds/leds-spi-byte.c
@@ -96,6 +96,7 @@ static int spi_byte_probe(struct spi_device *spi)
if (!led)
return -ENOMEM;
+ child = of_get_next_available_child(dev_of_node(dev), NULL);
of_property_read_string(child, "label", &name);
strscpy(led->name, name, sizeof(led->name));
led->spi = spi;
@@ -106,7 +107,6 @@ static int spi_byte_probe(struct spi_device *spi)
led->ldev.max_brightness = led->cdef->max_value - led->cdef->off_value;
led->ldev.brightness_set_blocking = spi_byte_brightness_set_blocking;
- child = of_get_next_available_child(dev_of_node(dev), NULL);
state = of_get_property(child, "default-state", NULL);
if (state) {
if (!strcmp(state, "on")) {
--
2.52.0.351.gbe84eed79e-goog
The soundwire update_status() callback may be called multiple times with
the same ATTACHED status but initialisation should only be done when
transitioning from UNATTACHED to ATTACHED.
Fix the inverted hw_init flag which was set to false instead of true
after initialisation which defeats its purpose and may result in
repeated unnecessary initialisation.
Similarly, the initial state of the flag was also inverted so that the
codec would only be initialised and brought out of regmap cache only
mode if its status first transitions to UNATTACHED.
Fixes: aa21a7d4f68a ("ASoC: codecs: wsa884x: Add WSA884x family of speakers")
Cc: stable(a)vger.kernel.org # 6.5
Cc: Krzysztof Kozlowski <krzk(a)kernel.org>
Signed-off-by: Johan Hovold <johan(a)kernel.org>
---
sound/soc/codecs/wsa884x.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/sound/soc/codecs/wsa884x.c b/sound/soc/codecs/wsa884x.c
index 887edd2be705..6c6b497657d0 100644
--- a/sound/soc/codecs/wsa884x.c
+++ b/sound/soc/codecs/wsa884x.c
@@ -1534,7 +1534,7 @@ static void wsa884x_init(struct wsa884x_priv *wsa884x)
wsa884x_set_gain_parameters(wsa884x);
- wsa884x->hw_init = false;
+ wsa884x->hw_init = true;
}
static int wsa884x_update_status(struct sdw_slave *slave,
@@ -2109,7 +2109,6 @@ static int wsa884x_probe(struct sdw_slave *pdev,
/* Start in cache-only until device is enumerated */
regcache_cache_only(wsa884x->regmap, true);
- wsa884x->hw_init = true;
if (IS_REACHABLE(CONFIG_HWMON)) {
struct device *hwmon;
--
2.51.2
The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 8a0e4bdddd1c998b894d879a1d22f1e745606215
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025122925-victory-numeral-2346@gregkh' --subject-prefix 'PATCH 6.18.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 8a0e4bdddd1c998b894d879a1d22f1e745606215 Mon Sep 17 00:00:00 2001
From: Wei Yang <richard.weiyang(a)gmail.com>
Date: Thu, 6 Nov 2025 03:41:55 +0000
Subject: [PATCH] mm/huge_memory: merge uniform_split_supported() and
non_uniform_split_supported()
uniform_split_supported() and non_uniform_split_supported() share
significantly similar logic.
The only functional difference is that uniform_split_supported() includes
an additional check on the requested @new_order.
The reason for this check comes from the following two aspects:
* some file system or swap cache just supports order-0 folio
* the behavioral difference between uniform/non-uniform split
The behavioral difference between uniform split and non-uniform:
* uniform split splits folio directly to @new_order
* non-uniform split creates after-split folios with orders from
folio_order(folio) - 1 to new_order.
This means for non-uniform split or !new_order split we should check the
file system and swap cache respectively.
This commit unifies the logic and merge the two functions into a single
combined helper, removing redundant code and simplifying the split
support checking mechanism.
Link: https://lkml.kernel.org/r/20251106034155.21398-3-richard.weiyang@gmail.com
Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
Signed-off-by: Wei Yang <richard.weiyang(a)gmail.com>
Reviewed-by: Zi Yan <ziy(a)nvidia.com>
Cc: Zi Yan <ziy(a)nvidia.com>
Cc: "David Hildenbrand (Red Hat)" <david(a)kernel.org>
Cc: Baolin Wang <baolin.wang(a)linux.alibaba.com>
Cc: Barry Song <baohua(a)kernel.org>
Cc: Dev Jain <dev.jain(a)arm.com>
Cc: Lance Yang <lance.yang(a)linux.dev>
Cc: Liam Howlett <liam.howlett(a)oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com>
Cc: Nico Pache <npache(a)redhat.com>
Cc: Ryan Roberts <ryan.roberts(a)arm.com>
Cc: <stable(a)vger.kernel.org>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index b74708dc5b5f..19d4a5f52ca2 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -374,10 +374,8 @@ int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list
unsigned int new_order, bool unmapped);
int min_order_for_split(struct folio *folio);
int split_folio_to_list(struct folio *folio, struct list_head *list);
-bool uniform_split_supported(struct folio *folio, unsigned int new_order,
- bool warns);
-bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
- bool warns);
+bool folio_split_supported(struct folio *folio, unsigned int new_order,
+ enum split_type split_type, bool warns);
int folio_split(struct folio *folio, unsigned int new_order, struct page *page,
struct list_head *list);
@@ -408,7 +406,7 @@ static inline int split_huge_page_to_order(struct page *page, unsigned int new_o
static inline int try_folio_split_to_order(struct folio *folio,
struct page *page, unsigned int new_order)
{
- if (!non_uniform_split_supported(folio, new_order, /* warns= */ false))
+ if (!folio_split_supported(folio, new_order, SPLIT_TYPE_NON_UNIFORM, /* warns= */ false))
return split_huge_page_to_order(&folio->page, new_order);
return folio_split(folio, new_order, page, NULL);
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4118f330c55e..d79a4bb363de 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3593,8 +3593,8 @@ static int __split_unmapped_folio(struct folio *folio, int new_order,
return 0;
}
-bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
- bool warns)
+bool folio_split_supported(struct folio *folio, unsigned int new_order,
+ enum split_type split_type, bool warns)
{
if (folio_test_anon(folio)) {
/* order-1 is not supported for anonymous THP. */
@@ -3602,48 +3602,41 @@ bool non_uniform_split_supported(struct folio *folio, unsigned int new_order,
"Cannot split to order-1 folio");
if (new_order == 1)
return false;
- } else if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
- !mapping_large_folio_support(folio->mapping)) {
- /*
- * No split if the file system does not support large folio.
- * Note that we might still have THPs in such mappings due to
- * CONFIG_READ_ONLY_THP_FOR_FS. But in that case, the mapping
- * does not actually support large folios properly.
- */
- VM_WARN_ONCE(warns,
- "Cannot split file folio to non-0 order");
- return false;
- }
-
- /* Only swapping a whole PMD-mapped folio is supported */
- if (folio_test_swapcache(folio)) {
- VM_WARN_ONCE(warns,
- "Cannot split swapcache folio to non-0 order");
- return false;
- }
-
- return true;
-}
-
-/* See comments in non_uniform_split_supported() */
-bool uniform_split_supported(struct folio *folio, unsigned int new_order,
- bool warns)
-{
- if (folio_test_anon(folio)) {
- VM_WARN_ONCE(warns && new_order == 1,
- "Cannot split to order-1 folio");
- if (new_order == 1)
- return false;
- } else if (new_order) {
+ } else if (split_type == SPLIT_TYPE_NON_UNIFORM || new_order) {
if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
!mapping_large_folio_support(folio->mapping)) {
+ /*
+ * We can always split a folio down to a single page
+ * (new_order == 0) uniformly.
+ *
+ * For any other scenario
+ * a) uniform split targeting a large folio
+ * (new_order > 0)
+ * b) any non-uniform split
+ * we must confirm that the file system supports large
+ * folios.
+ *
+ * Note that we might still have THPs in such
+ * mappings, which is created from khugepaged when
+ * CONFIG_READ_ONLY_THP_FOR_FS is enabled. But in that
+ * case, the mapping does not actually support large
+ * folios properly.
+ */
VM_WARN_ONCE(warns,
"Cannot split file folio to non-0 order");
return false;
}
}
- if (new_order && folio_test_swapcache(folio)) {
+ /*
+ * swapcache folio could only be split to order 0
+ *
+ * non-uniform split creates after-split folios with orders from
+ * folio_order(folio) - 1 to new_order, making it not suitable for any
+ * swapcache folio split. Only uniform split to order-0 can be used
+ * here.
+ */
+ if ((split_type == SPLIT_TYPE_NON_UNIFORM || new_order) && folio_test_swapcache(folio)) {
VM_WARN_ONCE(warns,
"Cannot split swapcache folio to non-0 order");
return false;
@@ -3711,11 +3704,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
if (new_order >= old_order)
return -EINVAL;
- if (split_type == SPLIT_TYPE_UNIFORM && !uniform_split_supported(folio, new_order, true))
- return -EINVAL;
-
- if (split_type == SPLIT_TYPE_NON_UNIFORM &&
- !non_uniform_split_supported(folio, new_order, true))
+ if (!folio_split_supported(folio, new_order, split_type, /* warn = */ true))
return -EINVAL;
is_hzp = is_huge_zero_folio(folio);
Hi Greg, Sasha,
Please consider commit ba1b40ed0e34 ("drm: nova: depend on
CONFIG_64BIT") for 6.18.y. It should cherry-pick cleanly.
Without this commit, one can create a config where `CONFIG_DRM_NOVA`
selects `CONFIG_NOVA_CORE` without satisfying its `CONFIG_64BIT`
dependency.
In turn, this means arm32 builds can fail -- Kconfig warns:
WARNING: unmet direct dependencies detected for NOVA_CORE
Depends on [n]: HAS_IOMEM [=y] && 64BIT && PCI [=y] && RUST [=y]
&& RUST_FW_LOADER_ABSTRACTIONS [=y]
Selected by [y]:
- DRM_NOVA [=y] && HAS_IOMEM [=y] && DRM [=y]=y [=y] && PCI [=y]
&& RUST [=y]
And then the build fails with (among others, see the related commit
5c5a41a75452 ("gpu: nova-core: depend on CONFIG_64BIT") for more):
error[E0308]: mismatched types
--> drivers/gpu/nova-core/fb.rs:50:59
|
50 | hal::fb_hal(chipset).write_sysmem_flush_page(bar,
page.dma_handle())?;
| -----------------------
^^^^^^^^^^^^^^^^^ expected `u64`, found `u32`
| |
| arguments to this method are incorrect
|
Cc'ing Danilo and Alexandre so that they can confirm they agree.
Thanks!
Cheers,
Miguel
Hi -
a Gentoo user recently found that 6.18.2 started to reproducuibly
crash when building their go toolchain [1].
Apparently the addition of "sched/fair: Forfeit vruntime on yield"
(mainline 79104becf42b) can result in the infamous NULL returned from
pick_eevdf(), which is not supposed to happen.
It turned out that the mentioned commit triggered a bug related
to the recently added proxy execution feature, which was already
fixed in mainline by "sched/proxy: Yield the donor task"
(127b90315ca0), though not marked for stable.
Applying this to 6.18.2/.3-rc1 (and probably 6.12 as well)
has reproducibly fixed the problem. A possible reason the crash
was triggered by the Go runtime could be its specific use of yield(),
though that's just speculation on my part.
So please add 127b90315ca0 ("sched/proxy: Yield the donor task")
to 6.18.y/6.12.y. I know we're already in 6.18.3-rc1, but the
crasher seems reproducible.
Fernand, please correct me if I got the explanations wrong.
Thanks!
Holger
[1] https://bugs.gentoo.org/968116 starting at #8