5.4-stable review patch. If anyone has any objections, please let me know.
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From: David Gow davidgow@google.com
commit 69b50d4351ed924f29e3d46b159e28f70dfc707f upstream.
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@google.com Fixes: dba79c3df4a2 ("arm: use generic mmap top-down layout and brk randomization") Signed-off-by: David Gow davidgow@google.com Reviewed-by: Kees Cook kees@kernel.org Cc: Alexandre Ghiti alex@ghiti.fr Cc: Linus Walleij linus.walleij@linaro.org Cc: Luis Chamberlain mcgrof@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Russell King linux@armlinux.org.uk Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/util.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/util.c +++ b/mm/util.c @@ -407,7 +407,7 @@ 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;