> Date: Mon, 21 Mar 2022 19:56:14 +0000 > From: Miod Vallat <[email protected]> > > A long, long time ago (I think it was late 2003), OpenBSD/i386 was > vulnerable to a trusted-yet-NULL pointer dereference in the agp code. > The attack involved using mmap(2) with MAP_FIXED and a hint of zero. > > Shortly afterwards, in addition to fixing the overtrusting code, it was > decided never to allow mmap(2) to allow address zero to get mapped, by > never making VM_MIN_ADDRESS equal to zero (I actually argued for this > change to only be applied to platforms with shared kernel/userland > address spaces, but the party's line prevailed), which is why > VM_MIN_ADDRESS is nowadays PAGE_SIZE instead of zero. > > Except on riscv64. > > The following diff adjusts VM_MIN_ADDRESS to follow the party's line. > > Completely untested due to lack of hardware.
Bleah, I thought we fixed that already. kernel boots; ok kettenis@ > Index: vmparam.h > =================================================================== > RCS file: /OpenBSD/src/sys/arch/riscv64/include/vmparam.h,v > retrieving revision 1.5 > diff -u -p -r1.5 vmparam.h > --- vmparam.h 2 Jul 2021 10:42:22 -0000 1.5 > +++ vmparam.h 21 Mar 2022 19:49:00 -0000 > @@ -111,8 +111,7 @@ > * VM_MIN_USER_ADDRESS and VM_MAX_USER_ADDRESS define the start and end of > the > * user address space. > */ > -// XXX OpenBSD/arm64 starts VM_MIN_ADDRESS from PAGE_SIZE. Why? > -#define VM_MIN_ADDRESS (0x0000000000000000UL) > +#define VM_MIN_ADDRESS ((vaddr_t)PAGE_SIZE) > #define VM_MAX_ADDRESS (0xffffffffffffffffUL) > > #define VM_MIN_KERNEL_ADDRESS (0xffffffc000000000UL) > >
