linux-kernel - [PATCH 6/8] stackleak: remove redundant check

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Date:   Mon, 25 Apr 2022 12:56:01 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, alex.popov@...ux.com,
        catalin.marinas@....com, keescook@...omium.org,
        linux-arm-kernel@...ts.infradead.org, luto@...nel.org,
        mark.rutland@....com, will@...nel.org
Subject: [PATCH 6/8] stackleak: remove redundant check

In __stackleak_erase() we check that the `erase_low` value derived from
`current->lowest_stack` is above the lowest legitimate stack pointer
value, but this is already enforced by stackleak_track_stack() when
recording the lowest stack value.

Remove the redundant check.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Cc: Alexander Popov <alex.popov@...ux.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Kees Cook <keescook@...omium.org>
---
 kernel/stackleak.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/kernel/stackleak.c b/kernel/stackleak.c
index f597d3323729d..ba346d46218f5 100644
--- a/kernel/stackleak.c
+++ b/kernel/stackleak.c
@@ -79,10 +79,6 @@ static __always_inline void __stackleak_erase(void)
 	unsigned int poison_count = 0;
 	const unsigned int depth = STACKLEAK_SEARCH_DEPTH / sizeof(unsigned long);
 
-	/* Check that 'lowest_stack' value is sane */
-	if (unlikely(erase_low - task_stack_low >= THREAD_SIZE))
-		erase_low = task_stack_low;
-
 	/* Search for the poison value in the kernel stack */
 	while (erase_low > task_stack_low && poison_count <= depth) {
 		if (*(unsigned long *)erase_low == STACKLEAK_POISON)
-- 
2.30.2