[V5,08/10] x86/entry: Preserve PKRS MSR across exceptions

From: Ira Weiny <ira.weiny@intel.com>

From: Ira Weiny <ira.weiny@intel.com>

The PKRS MSR is not managed by XSAVE.  It is preserved through a context
switch but this support leaves exception handling code open to memory
accesses during exceptions.

2 possible places for preserving this state were considered,
irqentry_state_t or pt_regs.[1]  pt_regs was much more complicated and
was potentially fraught with unintended consequences.[2]  However, Andy
came up with a way to hide additional values on the stack which could be
accessed as "extended_pt_regs".[3]  This method allows for; any place
which has struct pt_regs can get access to the extra information; no
extra information is added to irq_state; and pt_regs is left intact for
compatibility with outside tools like BPF.

To simplify, the assembly code only adds space on the stack.  The
setting or use of any needed values are left to the C code.  While some
entry points may not use this space it is still added where ever pt_regs
is passed to the C code for consistency.

Each nested exception gets another copy of this extended space allowing
for any number of levels of exception handling.

In the assembly, a macro is defined to allow a central place to add
space for other uses should the need arise.

Finally export pkrs_{save_set|restore}_irq to the common code to allow
it to preserve the current task's PKRS in the new extended pt_regs if
enabled.

Peter, Thomas, Andy, Dave, and Dan all suggested parts of the patch or
aided in the development of the patch..

[1] https://lore.kernel.org/lkml/CALCETrVe1i5JdyzD_BcctxQJn+ZE3T38EFPgjxN1F577M36g+w@mail.gmail.com/
[2] https://lore.kernel.org/lkml/874kpxx4jf.fsf@nanos.tec.linutronix.de/#t
[3] https://lore.kernel.org/lkml/CALCETrUHwZPic89oExMMe-WyDY8-O3W68NcZvse3=PGW+iW5=w@mail.gmail.com/

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Suggested-by: Dan Williams <dan.j.williams@intel.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>

---
Changes from V4:
	Fix checkpatch errors

Changes from V3:
	Fix 0-day issues
	Move all extended regs stuff to pks.h
	From Dan Williams
		Move show_extended_regs_oops ifdefery to pks.h
		Remove a bad comment
		s/irq_save_set_pkrs/pkrs_save_set_irq
		s/irq_restore_pkrs/pkrs_restore_irq
		s/ARCH_HAS/ARCH_ENABLE_SUPERVISOR_PKEYS
	From Dave Hansen:
		remove extra macro parameter for most calls
		clarify with comments
		Add BUILD check for extend regs size
		use subq/addq vs push/pop
	From Dan Williams and Dave Hansen:
		Use a macro call to wrap the c function calls with
		push/pop extended_pt_regs
	From Dave Hansen:
		Guidance on where to find each of the pt_regs being
		passed to C code
	From Thomas Gleixner:
		Remove unnecessary noinstr's
	From Andy Lutomirski:
		Convert to using the extended pt_regs
		Add in showing pks on fault through the extended pt_regs

Changes from V1
	remove redundant irq_state->pkrs
		This value is only needed for the global tracking.  So
		it should be included in that patch and not in this one.

Changes from RFC V3
	Standardize on 'irq_state' variable name
	Per Dave Hansen
		irq_save_pkrs() -> irq_save_set_pkrs()
	Rebased based on clean up patch by Thomas Gleixner
		This includes moving irq_[save_set|restore]_pkrs() to
		the core as well.
---
 arch/x86/entry/calling.h               | 26 ++++++++++++
 arch/x86/entry/common.c                | 58 ++++++++++++++++++++++++++
 arch/x86/entry/entry_64.S              | 22 +++++-----
 arch/x86/entry/entry_64_compat.S       |  6 +--
 arch/x86/include/asm/pks.h             | 16 +++++++
 arch/x86/include/asm/processor-flags.h |  2 +
 arch/x86/kernel/head_64.S              |  7 ++--
 arch/x86/mm/fault.c                    |  3 ++
 include/linux/pkeys.h                  | 17 ++++++++
 kernel/entry/common.c                  | 14 ++++++-
 10 files changed, 152 insertions(+), 19 deletions(-)

Message ID	20210331191405.341999-9-ira.weiny@intel.com (mailing list archive)
State	New
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Series	PKS: Add Protection Key Supervisor support \| expand [V5,00/10] PKS: Add Protection Key Supervisor support [V5,01/10] x86/pkeys: Create pkeys_common.h [V5,02/10] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support [V5,03/10] x86/pks: Add additional PKEY helper macros [V5,04/10] x86/pks: Add PKS defines and Kconfig options [V5,05/10] x86/pks: Add PKS setup code [V5,06/10] x86/fault: Adjust WARN_ON for PKey fault [V5,07/10] x86/pks: Preserve the PKRS MSR on context switch [V5,08/10] x86/entry: Preserve PKRS MSR across exceptions [V5,09/10] x86/pks: Add PKS kernel API [V5,10/10] x86/pks: Add PKS test code

[V5,08/10] x86/entry: Preserve PKRS MSR across exceptions

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