[PATCH V8 21/44] x86/entry: Add auxiliary pt_regs space

ira.weiny
2022-01-27T17:55:57Z

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

The PKRS MSR is not managed by XSAVE. In order for the MSR to be saved
during an exception the current CPU MSR value needs to be saved
somewhere during the exception and restored when returning to the
previous context.

Two 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 any place which
has struct pt_regs to get access to the extra information with no extra
information being added to irq_state and pt_regs is left intact for
compatibility with outside tools like BPF.

Prepare the assembly code to add a hidden auxiliary pt_regs space. To
simplify, the assembly code only adds space on the stack. The use of
this space is left to the C code which is required to select
ARCH_HAS_PTREGS_AUXILIARY to enable this support.

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

Initially the space is left empty and results in no code changes because
ARCH_HAS_PTREGS_AUXILIARY is not set. Subsequent patches adding data to
pt_regs_auxiliary must set ARCH_HAS_PTREGS_AUXILIARY or a build failure
will occur. The use of ARCH_HAS_PTREGS_AUXILIARY also avoids the
introduction of 2 instructions (addq/subq) on every entry call when the
extra space is not needed.

32bit is specifically excluded.

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/

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: 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 for V8:
Exclude 32bit
Introduce ARCH_HAS_PTREGS_AUXILIARY to optimize this away when
not needed.
From Thomas
s/EXTENDED_PT_REGS_SIZE/PT_REGS_AUX_SIZE
Fix up PTREGS_AUX_SIZE macro to be based on the
structures and used in assembly code via the
nifty asm-offset macros
Bound calls into c code with [PUSH|POP]_RTREGS_AUXILIARY
instead of using a macro 'call'
Split this patch out and put the PKS specific stuff in a
separate patch

Changes for V7:
Rebased to 5.14 entry code
declare write_pkrs() in pks.h
s/INIT_PKRS_VALUE/pkrs_init_value
Remove unnecessary INIT_PKRS_VALUE def
s/pkrs_save_set_irq/pkrs_save_irq/
The inital value for exceptions is best managed
completely within the pkey code.
---
arch/x86/Kconfig | 4 ++++
arch/x86/entry/calling.h | 20 ++++++++++++++++++++
arch/x86/entry/entry_64.S | 22 ++++++++++++++++++++++
arch/x86/entry/entry_64_compat.S | 6 ++++++
arch/x86/include/asm/ptrace.h | 19 +++++++++++++++++++
arch/x86/kernel/asm-offsets_64.c | 15 +++++++++++++++
arch/x86/kernel/head_64.S | 6 ++++++
7 files changed, 92 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a30fe85e27ac..82342f27b218 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1877,6 +1877,10 @@ config X86_INTEL_MEMORY_PROTECTION_KEYS

If unsure, say y.

+config ARCH_HAS_PTREGS_AUXILIARY
+ depends on X86_64
+ bool
+
choice
prompt "TSX enable mode"
depends on CPU_SUP_INTEL
diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index a4c061fb7c6e..d0ebf9b069c9 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -63,6 +63,26 @@ For 32-bit we have the following conventions - kernel is built with
* for assembly code:
*/

+
+#ifdef CONFIG_ARCH_HAS_PTREGS_AUXILIARY
+
+.macro PUSH_PTREGS_AUXILIARY
+ /* add space for pt_regs_auxiliary */
+ subq $PTREGS_AUX_SIZE, %rsp
+.endm
+
+.macro POP_PTREGS_AUXILIARY
+ /* remove space for pt_regs_auxiliary */
+ addq $PTREGS_AUX_SIZE, %rsp
+.endm
+
+#else
+
+#define PUSH_PTREGS_AUXILIARY
+#define POP_PTREGS_AUXILIARY
+
+#endif
+
.macro PUSH_REGS rdx=%rdx rax=%rax save_ret=0
.if \save_ret
pushq %rsi /* pt_regs->si */
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 466df3e50276..0684a8093965 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -332,7 +332,9 @@ SYM_CODE_END(ret_from_fork)
movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
.endif

+ PUSH_PTREGS_AUXILIARY
call \cfunc
+ POP_PTREGS_AUXILIARY

jmp error_return
.endm
@@ -435,7 +437,9 @@ SYM_CODE_START(\asmsym)

movq %rsp, %rdi /* pt_regs pointer */

+ PUSH_PTREGS_AUXILIARY
call \cfunc
+ POP_PTREGS_AUXILIARY

jmp paranoid_exit

@@ -496,7 +500,9 @@ SYM_CODE_START(\asmsym)
* stack.
*/
movq %rsp, %rdi /* pt_regs pointer */
+ PUSH_PTREGS_AUXILIARY
call vc_switch_off_ist
+ POP_PTREGS_AUXILIARY
movq %rax, %rsp /* Switch to new stack */

UNWIND_HINT_REGS
@@ -507,7 +513,9 @@ SYM_CODE_START(\asmsym)

movq %rsp, %rdi /* pt_regs pointer */

+ PUSH_PTREGS_AUXILIARY
call kernel_\cfunc
+ POP_PTREGS_AUXILIARY

/*
* No need to switch back to the IST stack. The current stack is either
@@ -542,7 +550,9 @@ SYM_CODE_START(\asmsym)
movq %rsp, %rdi /* pt_regs pointer into first argument */
movq ORIG_RAX(%rsp), %rsi /* get error code into 2nd argument*/
movq $-1, ORIG_RAX(%rsp) /* no syscall to restart */
+ PUSH_PTREGS_AUXILIARY
call \cfunc
+ POP_PTREGS_AUXILIARY

jmp paranoid_exit

@@ -784,7 +794,9 @@ SYM_CODE_START_LOCAL(exc_xen_hypervisor_callback)
movq %rdi, %rsp /* we don't return, adjust the stack frame */
UNWIND_HINT_REGS

+ PUSH_PTREGS_AUXILIARY
call xen_pv_evtchn_do_upcall
+ POP_PTREGS_AUXILIARY

jmp error_return
SYM_CODE_END(exc_xen_hypervisor_callback)
@@ -984,7 +996,9 @@ SYM_CODE_START_LOCAL(error_entry)
/* Put us onto the real thread stack. */
popq %r12 /* save return addr in %12 */
movq %rsp, %rdi /* arg0 = pt_regs pointer */
+ PUSH_PTREGS_AUXILIARY
call sync_regs
+ POP_PTREGS_AUXILIARY
movq %rax, %rsp /* switch stack */
ENCODE_FRAME_POINTER
pushq %r12
@@ -1040,7 +1054,9 @@ SYM_CODE_START_LOCAL(error_entry)
* as if we faulted immediately after IRET.
*/
mov %rsp, %rdi
+ PUSH_PTREGS_AUXILIARY
call fixup_bad_iret
+ POP_PTREGS_AUXILIARY
mov %rax, %rsp
jmp .Lerror_entry_from_usermode_after_swapgs
SYM_CODE_END(error_entry)
@@ -1146,7 +1162,9 @@ SYM_CODE_START(asm_exc_nmi)

movq %rsp, %rdi
movq $-1, %rsi
+ PUSH_PTREGS_AUXILIARY
call exc_nmi
+ POP_PTREGS_AUXILIARY

/*
* Return back to user mode. We must *not* do the normal exit
@@ -1182,6 +1200,8 @@ SYM_CODE_START(asm_exc_nmi)
* +---------------------------------------------------------+
* | pt_regs |
* +---------------------------------------------------------+
+ * | (Optionally) pt_regs_extended |
+ * +---------------------------------------------------------+
*
* The "original" frame is used by hardware. Before re-enabling
* NMIs, we need to be done with it, and we need to leave enough
@@ -1358,7 +1378,9 @@ end_repeat_nmi:

movq %rsp, %rdi
movq $-1, %rsi
+ PUSH_PTREGS_AUXILIARY
call exc_nmi
+ POP_PTREGS_AUXILIARY

/* Always restore stashed CR3 value (see paranoid_entry) */
RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 0051cf5c792d..c6859d8acae4 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -136,7 +136,9 @@ SYM_INNER_LABEL(entry_SYSENTER_compat_after_hwframe, SYM_L_GLOBAL)
.Lsysenter_flags_fixed:

movq %rsp, %rdi
+ PUSH_PTREGS_AUXILIARY
call do_SYSENTER_32
+ POP_PTREGS_AUXILIARY
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
"jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
@@ -253,7 +255,9 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
UNWIND_HINT_REGS

movq %rsp, %rdi
+ PUSH_PTREGS_AUXILIARY
call do_fast_syscall_32
+ POP_PTREGS_AUXILIARY
/* XEN PV guests always use IRET path */
ALTERNATIVE "testl %eax, %eax; jz swapgs_restore_regs_and_return_to_usermode", \
"jmp swapgs_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV
@@ -410,6 +414,8 @@ SYM_CODE_START(entry_INT80_compat)
cld

movq %rsp, %rdi
+ PUSH_PTREGS_AUXILIARY
call do_int80_syscall_32
+ POP_PTREGS_AUXILIARY
jmp swapgs_restore_regs_and_return_to_usermode
SYM_CODE_END(entry_INT80_compat)
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 703663175a5a..79541682e7f7 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -2,11 +2,13 @@
#ifndef _ASM_X86_PTRACE_H
#define _ASM_X86_PTRACE_H

+#include <linux/container_of.h>
#include <asm/segment.h>
#include <asm/page_types.h>
#include <uapi/asm/ptrace.h>

#ifndef __ASSEMBLY__
+
#ifdef __i386__

struct pt_regs {
@@ -91,6 +93,23 @@ struct pt_regs {
/* top of stack page */
};

+/*
+ * NOTE: Features which add data to pt_regs_auxiliary must select
+ * ARCH_HAS_PTREGS_AUXILIARY. Failure to do so will result in a build failure.
+ */
+struct pt_regs_auxiliary {
+};
+
+struct pt_regs_extended {
+ struct pt_regs_auxiliary aux;
+ struct pt_regs pt_regs __aligned(8);
+};
+
+static inline struct pt_regs_extended *to_extended_pt_regs(struct pt_regs *regs)
+{
+ return container_of(regs, struct pt_regs_extended, pt_regs);
+}
+
#endif /* !__i386__ */

#ifdef CONFIG_PARAVIRT
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index b14533af7676..66f08ac3507a 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -4,6 +4,7 @@
#endif

#include <asm/ia32.h>
+#include <asm/ptrace.h>

#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_PARAVIRT_SPINLOCKS)
#include <asm/kvm_para.h>
@@ -60,5 +61,19 @@ int main(void)
DEFINE(stack_canary_offset, offsetof(struct fixed_percpu_data, stack_canary));
BLANK();
#endif
+
+#ifdef CONFIG_ARCH_HAS_PTREGS_AUXILIARY
+ /* Size of Auxiliary pt_regs data */
+ DEFINE(PTREGS_AUX_SIZE, sizeof(struct pt_regs_extended) -
+ sizeof(struct pt_regs));
+#else
+ /*
+ * Adding data to struct pt_regs_auxiliary requires setting
+ * ARCH_HAS_PTREGS_AUXILIARY
+ */
+ BUILD_BUG_ON((sizeof(struct pt_regs_extended) -
+ sizeof(struct pt_regs)) != 0);
+#endif
+
return 0;
}
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 9c63fc5988cd..8418d9de8d70 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -336,8 +336,10 @@ SYM_CODE_START_NOALIGN(vc_boot_ghcb)
movq %rsp, %rdi
movq ORIG_RAX(%rsp), %rsi
movq initial_vc_handler(%rip), %rax
+ PUSH_PTREGS_AUXILIARY
ANNOTATE_RETPOLINE_SAFE
call *%rax
+ POP_PTREGS_AUXILIARY

/* Unwind pt_regs */
POP_REGS
@@ -414,7 +416,9 @@ SYM_CODE_START_LOCAL(early_idt_handler_common)
UNWIND_HINT_REGS

movq %rsp,%rdi /* RDI = pt_regs; RSI is already trapnr */
+ PUSH_PTREGS_AUXILIARY
call do_early_exception
+ POP_PTREGS_AUXILIARY

decl early_recursion_flag(%rip)
jmp restore_regs_and_return_to_kernel
@@ -438,7 +442,9 @@ SYM_CODE_START_NOALIGN(vc_no_ghcb)
/* Call C handler */
movq %rsp, %rdi
movq ORIG_RAX(%rsp), %rsi
+ PUSH_PTREGS_AUXILIARY
call do_vc_no_ghcb
+ POP_PTREGS_AUXILIARY

/* Unwind pt_regs */
POP_REGS
--
2.31.1