The patch titled
Subject: mm: only enforce minimum stack gap size if it's sensible
has been added to the -mm mm-unstable branch. Its filename is
mm-only-enforce-minimum-stack-gap-size-if-its-sensible.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-only-enforce-minimum-stack-gap-size-if-its-sensible.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: David Gow <davidgow@xxxxxxxxxx>
Subject: mm: only enforce minimum stack gap size if it's sensible
Date: Sat, 3 Aug 2024 15:46:41 +0800
The generic mmap_base code tries to leave a gap between the top of the
stack and the mmap base address, but enforces a minimum gap size (MIN_GAP)
of 128MB, which is too large on some setups. In particular, on arm tasks
without ADDR_LIMIT_32BIT, the STACK_TOP value is less than 128MB, so it's
impossible to fit such a gap in.
Only enforce this minimum if MIN_GAP < MAX_GAP, as we'd prefer to honour
MAX_GAP, which is defined proportionally, so scales better and always
leaves us with both _some_ stack space and some room for mmap.
This fixes the usercopy KUnit test suite on 32-bit arm, as it doesn't set
any personality flags so gets the default (in this case 26-bit) task size.
This test can be run with: ./tools/testing/kunit/kunit.py run --arch arm
usercopy --make_options LLVM=1
Link: https://lkml.kernel.org/r/20240803074642.1849623-2-davidgow@xxxxxxxxxx
Fixes: dba79c3df4a2 ("arm: use generic mmap top-down layout and brk randomization")
Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
Cc: Alexandre Ghiti <alex@xxxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxx>
Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/util.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/util.c~mm-only-enforce-minimum-stack-gap-size-if-its-sensible
+++ a/mm/util.c
@@ -463,7 +463,7 @@ static unsigned long mmap_base(unsigned
if (gap + pad > gap)
gap += pad;
- if (gap < MIN_GAP)
+ if (gap < MIN_GAP && MIN_GAP < MAX_GAP)
gap = MIN_GAP;
else if (gap > MAX_GAP)
gap = MAX_GAP;
_
Patches currently in -mm which might be from davidgow@xxxxxxxxxx are
mm-only-enforce-minimum-stack-gap-size-if-its-sensible.patch
