Under FRED, SETSSBSY is unavailable, and we want to be setting up FRED prior
to setting up shadow stacks. Luckily, RSTORSSP will also work in this case.
This involves a new type of shadow stack token, the Restore Token, which is
distinguished from the Supervisor Token by pointing to the adjacent slot on
the shadow stack rather than pointing at itself.
In the short term, this logic still needs to load MSR_PL0_SSP.
No functional change.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
---
xen/arch/x86/acpi/wakeup_prot.S | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)
diff --git a/xen/arch/x86/acpi/wakeup_prot.S b/xen/arch/x86/acpi/wakeup_prot.S
index dfc8c6ac6e8c..6ddc4011d8b6 100644
--- a/xen/arch/x86/acpi/wakeup_prot.S
+++ b/xen/arch/x86/acpi/wakeup_prot.S
@@ -90,7 +90,7 @@ LABEL(s3_resume)
mov %rcx, STACK_CPUINFO_FIELD(cr4)(%r15)
mov %rcx, %cr4
- /* WARNING! call/ret now fatal (iff SHSTK) until SETSSBSY loads SSP */
+ /* WARNING! CALL/RET now fatal (iff SHSTK) until RSTORSSP loads SSP */
#if defined(CONFIG_XEN_SHSTK)
test $CET_SHSTK_EN, %al
@@ -98,32 +98,31 @@ LABEL(s3_resume)
/*
* Restoring SSP is a little complicated, because we are intercepting
- * an in-use shadow stack. Write a temporary token under the stack,
- * so SETSSBSY will successfully load a value useful for us, then
- * reset MSR_PL0_SSP to its usual value and pop the temporary token.
+ * an in-use shadow stack. Write a Restore Token under the stack, and
+ * use RSTORSSP to load it. RSTORSSP converts the token to a
+ * Previous-SSP Token, which we discard.
*/
mov saved_ssp(%rip), %rdi
- /* Construct the temporary supervisor token under SSP. */
- sub $8, %rdi
-
- /* Load it into MSR_PL0_SSP. */
+ /* Calculate MSR_PL0_SSP from SSP. */
mov $MSR_PL0_SSP, %ecx
mov %rdi, %rdx
shr $32, %rdx
mov %edi, %eax
- wrmsr
-
- /* Write the temporary token onto the shadow stack, and activate it. */
- wrssq %rdi, (%rdi)
- setssbsy
-
- /* Reset MSR_PL0_SSP back to its normal value. */
and $~(STACK_SIZE - 1), %eax
or $(PRIMARY_SHSTK_SLOT + 1) * PAGE_SIZE - 8, %eax
wrmsr
- /* Pop the temporary token off the stack. */
+ /*
+ * A Restore Token's value is &token + 8 + 64BIT (bit 0).
+ * We want to put this on the shstk at SSP - 8.
+ */
+ lea 1(%rdi), %rax
+ sub $8, %rdi
+ wrssq %rax, (%rdi)
+ rstorssp (%rdi)
+
+ /* Discard the Previous-SSP Token from the shstk. */
mov $2, %eax
incsspd %eax
#endif /* CONFIG_XEN_SHSTK */
--
2.39.5
