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kernel/vm: Cleanups and minor fixes to get_area_page_protection.

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* We should not assume all non-kernel areas have KERNEL_READ_AREA
   permission, but follow the other permission flags directly.
   This way the kernel will be blocked from accessing guard pages, too.

 * Compute kernelProtection only once, and either return it directly
   or return it OR'd with the user protections.

Change-Id: Id6daa1cd15eb3102e23f95c08672ad97344e0722
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5096
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
This commit is contained in:
Augustin Cavalier 2022-03-11 14:20:50 -05:00 committed by waddlesplash
parent 4c51faeb59
commit a09dd6bb6c
1 changed files with 8 additions and 10 deletions
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18
src/system/kernel/vm/vm.cpp
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@ -505,19 +505,17 @@ get_area_page_protection(VMArea* area, addr_t pageAddress)
else
protection >>= 4;
// If this is a kernel area we translate the user flags to kernel flags.
if (area->address_space == VMAddressSpace::Kernel()) {
uint32 kernelProtection = 0;
if ((protection & B_READ_AREA) != 0)
kernelProtection |= B_KERNEL_READ_AREA;
if ((protection & B_WRITE_AREA) != 0)
kernelProtection |= B_KERNEL_WRITE_AREA;
uint32 kernelProtection = 0;
if ((protection & B_READ_AREA) != 0)
kernelProtection |= B_KERNEL_READ_AREA;
if ((protection & B_WRITE_AREA) != 0)
kernelProtection |= B_KERNEL_WRITE_AREA;
// If this is a kernel area we return only the kernel flags.
if (area->address_space == VMAddressSpace::Kernel())
return kernelProtection;
}
return protection | B_KERNEL_READ_AREA
| (protection & B_WRITE_AREA ? B_KERNEL_WRITE_AREA : 0);
return protection | kernelProtection;
}