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A direct write to a APxxKey_EL1 register requires a context
synchronization event to ensure that indirect reads made by subsequent
instructions (e.g. AUTIASP, PACIASP) observe the new value.
When we initialize the boot task's APIAKey in boot_init_stack_canary()
via ptrauth_keys_switch_kernel() we miss the necessary ISB, and so there
is a window where instructions are not guaranteed to use the new APIAKey
value. This has been observed to result in boot-time crashes where
PACIASP and AUTIASP within a function used a mixture of the old and new
key values.
Fix this by having ptrauth_keys_switch_kernel() synchronize the new key
value with an ISB. At the same time, __ptrauth_key_install() is renamed
to __ptrauth_key_install_nosync() so that it is obvious that this
performs no synchronization itself.
Fixes: 28321582334c261c ("arm64: initialize ptrauth keys for kernel booting task")
Signed-off-by: Mark Rutland <[email protected]>
Reported-by: Will Deacon <[email protected]>
Cc: Amit Daniel Kachhap <[email protected]>
Cc: Marc Zyngier <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
Tested-by: Will Deacon <[email protected]>
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Functions like vmap() record how much memory has been allocated by their
callers, and callers are identified using __builtin_return_address(). Once
the kernel is using pointer-auth the return address will be signed. This
means it will not match any kernel symbol, and will vary between threads
even for the same caller.
The output of /proc/vmallocinfo in this case may look like,
0x(____ptrval____)-0x(____ptrval____) 20480 0x86e28000100e7c60 pages=4 vmalloc N0=4
0x(____ptrval____)-0x(____ptrval____) 20480 0x86e28000100e7c60 pages=4 vmalloc N0=4
0x(____ptrval____)-0x(____ptrval____) 20480 0xc5c78000100e7c60 pages=4 vmalloc N0=4
The above three 64bit values should be the same symbol name and not
different LR values.
Use the pre-processor to add logic to clear the PAC to
__builtin_return_address() callers. This patch adds a new file
asm/compiler.h and is transitively included via include/compiler_types.h on
the compiler command line so it is guaranteed to be loaded and the users of
this macro will not find a wrong version.
Helper macros ptrauth_kernel_pac_mask/ptrauth_clear_pac are created for
this purpose and added in this file. Existing macro ptrauth_user_pac_mask
moved from asm/pointer_auth.h.
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Reviewed-by: James Morse <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
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This patch uses the existing boot_init_stack_canary arch function
to initialize the ptrauth keys for the booting task in the primary
core. The requirement here is that it should be always inline and
the caller must never return.
As pointer authentication too detects a subset of stack corruption
so it makes sense to place this code here.
Both pointer authentication and stack canary codes are protected
by their respective config option.
Suggested-by: Ard Biesheuvel <[email protected]>
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
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Set up keys to use pointer authentication within the kernel. The kernel
will be compiled with APIAKey instructions, the other keys are currently
unused. Each task is given its own APIAKey, which is initialized during
fork. The key is changed during context switch and on kernel entry from
EL0.
The keys for idle threads need to be set before calling any C functions,
because it is not possible to enter and exit a function with different
keys.
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
[Amit: Modified secondary cores key structure, comments]
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
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As we're going to enable pointer auth within the kernel and use a
different APIAKey for the kernel itself, so move the user APIAKey
switch to EL0 exception return.
The other 4 keys could remain switched during task switch, but are also
moved to keep things consistent.
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: James Morse <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
[Amit: commit msg, re-positioned the patch, comments]
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
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We currently enable ptrauth for userspace, but do not use it within the
kernel. We're going to enable it for the kernel, and will need to manage
a separate set of ptrauth keys for the kernel.
We currently keep all 5 keys in struct ptrauth_keys. However, as the
kernel will only need to use 1 key, it is a bit wasteful to allocate a
whole ptrauth_keys struct for every thread.
Therefore, a subsequent patch will define a separate struct, with only 1
key, for the kernel. In preparation for that, rename the existing struct
(and associated macros and functions) to reflect that they are specific
to userspace.
Acked-by: Catalin Marinas <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
[Amit: Re-positioned the patch to reduce the diff]
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
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Previous patches have enabled 52-bit kernel + user VAs and there is no
longer any scenario where user VA != kernel VA size.
This patch removes the, now redundant, vabits_user variable and replaces
usage with vabits_actual where appropriate.
Reviewed-by: Catalin Marinas <[email protected]>
Signed-off-by: Steve Capper <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
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This patch corrects the SPDX License Identifier style
in the arm64 Hardware Architecture related files.
Suggested-by: Joe Perches <[email protected]>
Signed-off-by: Nishad Kamdar <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
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We don't need to get at the per-thread keys from assembly at all, so
they can live alongside the rest of the per-thread register state in
thread_struct instead of thread_info.
This will also allow straighforward whitelisting of the keys for
hardened usercopy should we expose them via a ptrace request later on.
Signed-off-by: Will Deacon <[email protected]>
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Add an arm64-specific prctl to allow a thread to reinitialize its
pointer authentication keys to random values. This can be useful when
exec() is not used for starting new processes, to ensure that different
processes still have different keys.
Signed-off-by: Kristina Martsenko <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
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When the kernel is unwinding userspace callchains, we can't expect that
the userspace consumer of these callchains has the data necessary to
strip the PAC from the stored LR.
This patch has the kernel strip the PAC from user stackframes when the
in-kernel unwinder is used. This only affects the LR value, and not the
FP.
This only affects the in-kernel unwinder. When userspace performs
unwinding, it is up to userspace to strip PACs as necessary (which can
be determined from DWARF information).
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Ramana Radhakrishnan <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Will Deacon <[email protected]>
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When pointer authentication is in use, data/instruction pointers have a
number of PAC bits inserted into them. The number and position of these
bits depends on the configured TCR_ELx.TxSZ and whether tagging is
enabled. ARMv8.3 allows tagging to differ for instruction and data
pointers.
For userspace debuggers to unwind the stack and/or to follow pointer
chains, they need to be able to remove the PAC bits before attempting to
use a pointer.
This patch adds a new structure with masks describing the location of
the PAC bits in userspace instruction and data pointers (i.e. those
addressable via TTBR0), which userspace can query via PTRACE_GETREGSET.
By clearing these bits from pointers (and replacing them with the value
of bit 55), userspace can acquire the PAC-less versions.
This new regset is exposed when the kernel is built with (user) pointer
authentication support, and the address authentication feature is
enabled. Otherwise, the regset is hidden.
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Ramana Radhakrishnan <[email protected]>
Cc: Will Deacon <[email protected]>
[will: Fix to use vabits_user instead of VA_BITS and rename macro]
Signed-off-by: Will Deacon <[email protected]>
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This patch adds basic support for pointer authentication, allowing
userspace to make use of APIAKey, APIBKey, APDAKey, APDBKey, and
APGAKey. The kernel maintains key values for each process (shared by all
threads within), which are initialised to random values at exec() time.
The ID_AA64ISAR1_EL1.{APA,API,GPA,GPI} fields are exposed to userspace,
to describe that pointer authentication instructions are available and
that the kernel is managing the keys. Two new hwcaps are added for the
same reason: PACA (for address authentication) and PACG (for generic
authentication).
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Kristina Martsenko <[email protected]>
Tested-by: Adam Wallis <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Ramana Radhakrishnan <[email protected]>
Cc: Suzuki K Poulose <[email protected]>
Cc: Will Deacon <[email protected]>
[will: Fix sizeof() usage and unroll address key initialisation]
Signed-off-by: Will Deacon <[email protected]>
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