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H A Dpm_machdep.cdiff 210595 Thu Jul 29 02:39:46 MDT 2010 jmallett o) Subtract 64K from the default userland stack pointer. GCC generate code
that with a 32-bit ABI on a system with 64-bit registers can attempt to
access an invalid (well, kernel) memory address rather than the intended
user address for stack-relative loads and stores. Lowering the stack
pointer works around this. [1]
o) Make TRAP_DEBUG code conditional on the trap_debug variable. Make
trap_debug default to 0 instead of 1 now but make it possible to change it
at runtime using sysctl.
o) Kill programs that attempt an unaligned access of a kernel address. Note
that with some ABIs, calling useracc() is not sufficient since the register
may be 64-bit but vm_offset_t is 32-bit so a kernel address could be
truncated to what looks like a valid user address, allowing the user to
crash the kernel.
o) Clean up unaligned access emulation to support unaligned 16-bit and 64-bit
accesses. (For 16-bit accesses it was checking for user access to too much
memory (4 bytes) and there was no 64-bit support.) This still lacks support
for unaligned load-linked and store-conditional.

Reviewed by: [1] gonzo
H A Dtrap.cdiff 210595 Thu Jul 29 02:39:46 MDT 2010 jmallett o) Subtract 64K from the default userland stack pointer. GCC generate code
that with a 32-bit ABI on a system with 64-bit registers can attempt to
access an invalid (well, kernel) memory address rather than the intended
user address for stack-relative loads and stores. Lowering the stack
pointer works around this. [1]
o) Make TRAP_DEBUG code conditional on the trap_debug variable. Make
trap_debug default to 0 instead of 1 now but make it possible to change it
at runtime using sysctl.
o) Kill programs that attempt an unaligned access of a kernel address. Note
that with some ABIs, calling useracc() is not sufficient since the register
may be 64-bit but vm_offset_t is 32-bit so a kernel address could be
truncated to what looks like a valid user address, allowing the user to
crash the kernel.
o) Clean up unaligned access emulation to support unaligned 16-bit and 64-bit
accesses. (For 16-bit accesses it was checking for user access to too much
memory (4 bytes) and there was no 64-bit support.) This still lacks support
for unaligned load-linked and store-conditional.

Reviewed by: [1] gonzo

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