On 6 September 2015 at 10:15, Heyi Guo <[email protected]> wrote:
> There is a hidden bug for below code:
>
> (1 << BaseAddressAlignment) & *BlockEntrySize
>
> From disassembly code, we can the literal number 1 will be treated as
> INT32 by compiler by default, and we'll get 0xFFFFFFFF80000000 when
> BaseAddressAlignment is equal to 31. So we will always get 31 when
> alignment is larger than 31.
>
> if ((1 << BaseAddressAlignment) & *BlockEntrySize) {
> 5224: f9404be0 ldr x0, [sp,#144]
> 5228: 2a0003e1 mov w1, w0
> 522c: 52800020 mov w0, #0x1 // #1
> 5230: 1ac12000 lsl w0, w0, w1
> 5234: 93407c01 sxtw x1, w0
>
> The bug can be replayed on QEMU AARCH64; by adding some debug print,
> we can see lots of level 1 tables created (for block of 1GB) even
> when the region is large enough to use 512GB block size.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Heyi Guo <[email protected]>
> Cc: Leif Lindholm <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
> ---
> ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
> b/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
> index e7b095c..b039ae1 100644
> --- a/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
> +++ b/ArmPkg/Library/ArmLib/AArch64/AArch64Mmu.c
> @@ -295,14 +295,16 @@ GetBlockEntryListFromAddress (
> if (RegionStart == 0) {
> // Identify the highest possible alignment for the Region Size
> for (BaseAddressAlignment = 0; BaseAddressAlignment < 64;
> BaseAddressAlignment++) {
> - if ((1 << BaseAddressAlignment) & *BlockEntrySize) {
> + // Type casting is needed as literal number will be treated as INT32 by
> + // compiler
> + if (((UINT64) 1 << BaseAddressAlignment) & *BlockEntrySize) {
Please use '1UL' instead of '(UINT64) 1'
> break;
> }
> }
> } else {
> // Identify the highest possible alignment for the Base Address
> for (BaseAddressAlignment = 0; BaseAddressAlignment < 64;
> BaseAddressAlignment++) {
> - if ((1 << BaseAddressAlignment) & RegionStart) {
> + if (((UINT64) 1 << BaseAddressAlignment) & RegionStart) {
> break;
> }
> }
> --
> 2.5.0
>
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