5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Gow <davidgow@xxxxxxxxxx> 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@xxxxxxxxxx Fixes: dba79c3df4a2 ("arm: use generic mmap top-down layout and brk randomization") Signed-off-by: David Gow <davidgow@xxxxxxxxxx> Reviewed-by: Kees Cook <kees@xxxxxxxxxx> Cc: Alexandre Ghiti <alex@xxxxxxxx> 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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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;
