From: Mark Rutland <mark.rutland@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: akpm@linux-foundation.org, alex.popov@linux.com,
catalin.marinas@arm.com, keescook@chromium.org,
linux-kernel@vger.kernel.org, luto@kernel.org,
mark.rutland@arm.com, will@kernel.org
Subject: [PATCH v2 05/13] stackleak: clarify variable names
Date: Wed, 27 Apr 2022 18:31:20 +0100 [thread overview]
Message-ID: <20220427173128.2603085-6-mark.rutland@arm.com> (raw)
In-Reply-To: <20220427173128.2603085-1-mark.rutland@arm.com>
The logic within __stackleak_erase() can be a little hard to follow, as
`boundary` switches from being the low bound to the high bound mid way
through the function, and `kstack_ptr` is used to represent the start of
the region to erase while `boundary` represents the end of the region to
erase.
Make this a little clearer by consistently using clearer variable names.
The `boundary` variable is removed, the bounds of the region to erase
are described by `erase_low` and `erase_high`, and bounds of the task
stack are described by `task_stack_low` and `task_stck_high`.
As the same time, remove the comment above the variables, since it is
unclear whether it's intended as rationale, a complaint, or a TODO, and
is more confusing than helpful.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Popov <alex.popov@linux.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
---
kernel/stackleak.c | 30 ++++++++++++++----------------
1 file changed, 14 insertions(+), 16 deletions(-)
diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index 24b7cf01b2972..d5f684dc0a2d9 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -73,40 +73,38 @@ late_initcall(stackleak_sysctls_init);
static __always_inline void __stackleak_erase(void)
{
const unsigned long task_stack_low = stackleak_task_low_bound(current);
-
- /* It would be nice not to have 'kstack_ptr' and 'boundary' on stack */
- unsigned long kstack_ptr = current->lowest_stack;
- unsigned long boundary = task_stack_low;
+ unsigned long erase_low = current->lowest_stack;
+ unsigned long erase_high;
unsigned int poison_count = 0;
const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
/* Search for the poison value in the kernel stack */
- while (kstack_ptr > boundary && poison_count <= depth) {
- if (*(unsigned long *)kstack_ptr == STACKLEAK_POISON)
+ while (erase_low > task_stack_low && poison_count <= depth) {
+ if (*(unsigned long *)erase_low == STACKLEAK_POISON)
poison_count++;
else
poison_count = 0;
- kstack_ptr -= sizeof(unsigned long);
+ erase_low -= sizeof(unsigned long);
}
#ifdef CONFIG_STACKLEAK_METRICS
- current->prev_lowest_stack = kstack_ptr;
+ current->prev_lowest_stack = erase_low;
#endif
/*
- * Now write the poison value to the kernel stack. Start from
- * 'kstack_ptr' and move up till the new 'boundary'. We assume that
- * the stack pointer doesn't change when we write poison.
+ * Now write the poison value to the kernel stack between 'erase_low'
+ * and 'erase_high'. We assume that the stack pointer doesn't change
+ * when we write poison.
*/
if (on_thread_stack())
- boundary = current_stack_pointer;
+ erase_high = current_stack_pointer;
else
- boundary = current_top_of_stack();
+ erase_high = current_top_of_stack();
- while (kstack_ptr < boundary) {
- *(unsigned long *)kstack_ptr = STACKLEAK_POISON;
- kstack_ptr += sizeof(unsigned long);
+ while (erase_low < erase_high) {
+ *(unsigned long *)erase_low = STACKLEAK_POISON;
+ erase_low += sizeof(unsigned long);
}
/* Reset the 'lowest_stack' value for the next syscall */
--
2.30.2
next prev parent reply other threads:[~2022-04-27 17:32 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 17:31 [PATCH v2 00/13] stackleak: fixes and rework Mark Rutland
2022-04-27 17:31 ` [PATCH v2 01/13] arm64: stackleak: fix current_top_of_stack() Mark Rutland
2022-05-04 16:41 ` Catalin Marinas
2022-05-04 19:01 ` Kees Cook
2022-05-04 19:55 ` Catalin Marinas
2022-05-05 8:25 ` Will Deacon
2022-05-08 17:24 ` Alexander Popov
2022-05-10 11:36 ` Mark Rutland
2022-04-27 17:31 ` [PATCH v2 02/13] stackleak: move skip_erasing() check earlier Mark Rutland
2022-05-08 17:44 ` Alexander Popov
2022-05-10 11:40 ` Mark Rutland
2022-04-27 17:31 ` [PATCH v2 03/13] stackleak: remove redundant check Mark Rutland
2022-05-08 18:17 ` Alexander Popov
2022-05-10 11:46 ` Mark Rutland
2022-05-11 3:00 ` Kees Cook
2022-05-11 8:02 ` Mark Rutland
2022-05-11 14:44 ` Kees Cook
2022-05-12 9:14 ` Mark Rutland
2022-05-15 16:17 ` Alexander Popov
2022-05-24 10:03 ` Mark Rutland
2022-05-26 22:09 ` Alexander Popov
2022-04-27 17:31 ` [PATCH v2 04/13] stackleak: rework stack low bound handling Mark Rutland
2022-04-27 17:31 ` Mark Rutland [this message]
2022-05-08 20:49 ` [PATCH v2 05/13] stackleak: clarify variable names Alexander Popov
2022-05-10 13:01 ` Mark Rutland
2022-05-11 3:05 ` Kees Cook
2022-04-27 17:31 ` [PATCH v2 06/13] stackleak: rework stack high bound handling Mark Rutland
2022-05-08 21:27 ` Alexander Popov
2022-05-10 11:22 ` Mark Rutland
2022-05-15 16:32 ` Alexander Popov
2022-04-27 17:31 ` [PATCH v2 07/13] stackleak: rework poison scanning Mark Rutland
2022-05-09 13:51 ` Alexander Popov
2022-05-10 13:13 ` Mark Rutland
2022-05-15 17:33 ` Alexander Popov
2022-05-24 13:31 ` Mark Rutland
2022-05-26 23:25 ` Alexander Popov
2022-05-31 18:13 ` Kees Cook
2022-06-03 16:55 ` Alexander Popov
2022-04-27 17:31 ` [PATCH v2 08/13] lkdtm/stackleak: avoid spurious failure Mark Rutland
2022-04-27 17:31 ` [PATCH v2 09/13] lkdtm/stackleak: rework boundary management Mark Rutland
2022-05-04 19:07 ` Kees Cook
2022-04-27 17:31 ` [PATCH v2 10/13] lkdtm/stackleak: prevent unexpected stack usage Mark Rutland
2022-04-27 17:31 ` [PATCH v2 11/13] lkdtm/stackleak: check stack boundaries Mark Rutland
2022-04-27 17:31 ` [PATCH v2 12/13] stackleak: add on/off stack variants Mark Rutland
2022-04-27 17:31 ` [PATCH v2 13/13] arm64: entry: use stackleak_erase_on_task_stack() Mark Rutland
2022-05-04 16:42 ` Catalin Marinas
2022-05-04 19:16 ` [PATCH v2 00/13] stackleak: fixes and rework Kees Cook
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