On Mon, Jul 29, 2024 at 09:07:48PM -0700, Arjun wrote:
> Fixes support for 64-bit badram entries. Previously, whenever the start
> address
> of an mmap region exceeded the maximum address attainable via an addr,mask
> pair,
> GRUB would erroneously attempt to binary-search up to the integer limit for an
> unsigned 64-bit integer in search of the "start" of its iterator over badram
> locations in the current range.
>
> On its own this wouldn't be an issue, as the iterator should be empty anyway
> in
> this case. However, the binary search code directly adds two 64-bit unsigned
> integers as an intermediate step, causing an integer overflow and a subsequent
> infinite loop.
>
> This patch fixes this behavior with two changes:
> 1. We set the initial upper bound of the binary search to the actual maximum
> possible index for the iterator to start at (i.e. (1 << var) - 1), rather
> than the 64-bit unsigned integer limit.
> 2. We avoid any integer overflows in the binary search by adding the high
> and
> low operands more carefully.
>
> The user-facing effect of this is that 64-bit badram entries no longer cause
> GRUB to hang indefinitely. This change has been tested and verified working on
> x86_64 EFI.
Missing Signed-off-by: ...
> ---
> grub-core/mmap/mmap.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/grub-core/mmap/mmap.c b/grub-core/mmap/mmap.c
> index c8c8312c5..ce02d8e66 100644
> --- a/grub-core/mmap/mmap.c
> +++ b/grub-core/mmap/mmap.c
> @@ -396,13 +396,14 @@ badram_iter (grub_uint64_t addr, grub_uint64_t size,
> else
> {
> low = 0;
> - high = ~0ULL;
> + high = var < 64 ? (1ULL << var) - 1ULL : ~0ULL;
Instead of ULL you should use grub_uint64_t cast.
> /* Find starting value. Keep low and high such that
> fill_mask (low) < addr and fill_mask (high) >= addr;
> */
> while (high - low > 1)
> {
> - cur = (low + high) / 2;
> + cur = low / 2 + high / 2 + (low & high & 1ULL);
Ditto...
Daniel
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