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2d6bb6adb7
- Introduces the stackleak gcc plugin ported from grsecurity by Alexander
Popov, with x86 and arm64 support.
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Merge tag 'stackleak-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux
Pull stackleak gcc plugin from Kees Cook:
"Please pull this new GCC plugin, stackleak, for v4.20-rc1. This plugin
was ported from grsecurity by Alexander Popov. It provides efficient
stack content poisoning at syscall exit. This creates a defense
against at least two classes of flaws:
- Uninitialized stack usage. (We continue to work on improving the
compiler to do this in other ways: e.g. unconditional zero init was
proposed to GCC and Clang, and more plugin work has started too).
- Stack content exposure. By greatly reducing the lifetime of valid
stack contents, exposures via either direct read bugs or unknown
cache side-channels become much more difficult to exploit. This
complements the existing buddy and heap poisoning options, but
provides the coverage for stacks.
The x86 hooks are included in this series (which have been reviewed by
Ingo, Dave Hansen, and Thomas Gleixner). The arm64 hooks have already
been merged through the arm64 tree (written by Laura Abbott and
reviewed by Mark Rutland and Will Deacon).
With VLAs having been removed this release, there is no need for
alloca() protection, so it has been removed from the plugin"
* tag 'stackleak-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
arm64: Drop unneeded stackleak_check_alloca()
stackleak: Allow runtime disabling of kernel stack erasing
doc: self-protection: Add information about STACKLEAK feature
fs/proc: Show STACKLEAK metrics in the /proc file system
lkdtm: Add a test for STACKLEAK
gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack
x86/entry: Add STACKLEAK erasing the kernel stack at the end of syscalls
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====================================================
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Complete virtual memory map with 4-level page tables
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====================================================
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Notes:
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- Negative addresses such as "-23 TB" are absolute addresses in bytes, counted down
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from the top of the 64-bit address space. It's easier to understand the layout
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when seen both in absolute addresses and in distance-from-top notation.
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For example 0xffffe90000000000 == -23 TB, it's 23 TB lower than the top of the
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64-bit address space (ffffffffffffffff).
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Note that as we get closer to the top of the address space, the notation changes
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from TB to GB and then MB/KB.
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- "16M TB" might look weird at first sight, but it's an easier to visualize size
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notation than "16 EB", which few will recognize at first sight as 16 exabytes.
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It also shows it nicely how incredibly large 64-bit address space is.
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========================================================================================================================
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Start addr | Offset | End addr | Size | VM area description
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========================================================================================================================
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0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm
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__________________|____________|__________________|_________|___________________________________________________________
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0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -128 TB
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| | | | starting offset of kernel mappings.
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__________________|____________|__________________|_________|___________________________________________________________
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| Kernel-space virtual memory, shared between all processes:
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____________________________________________________________|___________________________________________________________
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ffff800000000000 | -128 TB | ffff87ffffffffff | 8 TB | ... guard hole, also reserved for hypervisor
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ffff880000000000 | -120 TB | ffffc7ffffffffff | 64 TB | direct mapping of all physical memory (page_offset_base)
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ffffc80000000000 | -56 TB | ffffc8ffffffffff | 1 TB | ... unused hole
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ffffc90000000000 | -55 TB | ffffe8ffffffffff | 32 TB | vmalloc/ioremap space (vmalloc_base)
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ffffe90000000000 | -23 TB | ffffe9ffffffffff | 1 TB | ... unused hole
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ffffea0000000000 | -22 TB | ffffeaffffffffff | 1 TB | virtual memory map (vmemmap_base)
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ffffeb0000000000 | -21 TB | ffffebffffffffff | 1 TB | ... unused hole
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ffffec0000000000 | -20 TB | fffffbffffffffff | 16 TB | KASAN shadow memory
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fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole
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| | | | vaddr_end for KASLR
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fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping
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fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | LDT remap for PTI
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ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks
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__________________|____________|__________________|_________|____________________________________________________________
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| Identical layout to the 47-bit one from here on:
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____________________________________________________________|____________________________________________________________
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ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole
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ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space
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ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole
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ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0
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ffffffff80000000 |-2048 MB | | |
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ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space
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ffffffffff000000 | -16 MB | | |
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FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset
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ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI
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ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole
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__________________|____________|__________________|_________|___________________________________________________________
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====================================================
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Complete virtual memory map with 5-level page tables
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====================================================
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Notes:
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- With 56-bit addresses, user-space memory gets expanded by a factor of 512x,
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from 0.125 PB to 64 PB. All kernel mappings shift down to the -64 PT starting
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offset and many of the regions expand to support the much larger physical
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memory supported.
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========================================================================================================================
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Start addr | Offset | End addr | Size | VM area description
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========================================================================================================================
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0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm
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__________________|____________|__________________|_________|___________________________________________________________
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0000800000000000 | +64 PB | ffff7fffffffffff | ~16K PB | ... huge, still almost 64 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -128 TB
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| | | | starting offset of kernel mappings.
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__________________|____________|__________________|_________|___________________________________________________________
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| Kernel-space virtual memory, shared between all processes:
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____________________________________________________________|___________________________________________________________
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ff00000000000000 | -64 PB | ff0fffffffffffff | 4 PB | ... guard hole, also reserved for hypervisor
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ff10000000000000 | -60 PB | ff8fffffffffffff | 32 PB | direct mapping of all physical memory (page_offset_base)
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ff90000000000000 | -28 PB | ff9fffffffffffff | 4 PB | LDT remap for PTI
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ffa0000000000000 | -24 PB | ffd1ffffffffffff | 12.5 PB | vmalloc/ioremap space (vmalloc_base)
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ffd2000000000000 | -11.5 PB | ffd3ffffffffffff | 0.5 PB | ... unused hole
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ffd4000000000000 | -11 PB | ffd5ffffffffffff | 0.5 PB | virtual memory map (vmemmap_base)
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ffd6000000000000 | -10.5 PB | ffdeffffffffffff | 2.25 PB | ... unused hole
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ffdf000000000000 | -8.25 PB | fffffdffffffffff | ~8 PB | KASAN shadow memory
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fffffc0000000000 | -4 TB | fffffdffffffffff | 2 TB | ... unused hole
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| | | | vaddr_end for KASLR
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fffffe0000000000 | -2 TB | fffffe7fffffffff | 0.5 TB | cpu_entry_area mapping
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fffffe8000000000 | -1.5 TB | fffffeffffffffff | 0.5 TB | ... unused hole
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ffffff0000000000 | -1 TB | ffffff7fffffffff | 0.5 TB | %esp fixup stacks
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__________________|____________|__________________|_________|____________________________________________________________
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| Identical layout to the 47-bit one from here on:
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____________________________________________________________|____________________________________________________________
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ffffff8000000000 | -512 GB | ffffffeeffffffff | 444 GB | ... unused hole
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ffffffef00000000 | -68 GB | fffffffeffffffff | 64 GB | EFI region mapping space
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ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | ... unused hole
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ffffffff80000000 | -2 GB | ffffffff9fffffff | 512 MB | kernel text mapping, mapped to physical address 0
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ffffffff80000000 |-2048 MB | | |
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ffffffffa0000000 |-1536 MB | fffffffffeffffff | 1520 MB | module mapping space
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ffffffffff000000 | -16 MB | | |
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FIXADDR_START | ~-11 MB | ffffffffff5fffff | ~0.5 MB | kernel-internal fixmap range, variable size and offset
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ffffffffff600000 | -10 MB | ffffffffff600fff | 4 kB | legacy vsyscall ABI
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ffffffffffe00000 | -2 MB | ffffffffffffffff | 2 MB | ... unused hole
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__________________|____________|__________________|_________|___________________________________________________________
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Architecture defines a 64-bit virtual address. Implementations can support
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less. Currently supported are 48- and 57-bit virtual addresses. Bits 63
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through to the most-significant implemented bit are sign extended.
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This causes hole between user space and kernel addresses if you interpret them
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as unsigned.
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The direct mapping covers all memory in the system up to the highest
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memory address (this means in some cases it can also include PCI memory
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holes).
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vmalloc space is lazily synchronized into the different PML4/PML5 pages of
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the processes using the page fault handler, with init_top_pgt as
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reference.
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We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual
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memory window (this size is arbitrary, it can be raised later if needed).
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The mappings are not part of any other kernel PGD and are only available
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during EFI runtime calls.
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Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
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physical memory, vmalloc/ioremap space and virtual memory map are randomized.
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Their order is preserved but their base will be offset early at boot time.
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Be very careful vs. KASLR when changing anything here. The KASLR address
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range must not overlap with anything except the KASAN shadow area, which is
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correct as KASAN disables KASLR.
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For both 4- and 5-level layouts, the STACKLEAK_POISON value in the last 2MB
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hole: ffffffffffff4111
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