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riscv: Permit spurious faults in kernel mode

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Right now, pmap_enter() does not issue an sfence.vma after overwriting
an invalid PTE, so the kernel can trigger a page fault when accessing a
freshly created mapping.  In this case, pmap_fault() can handle the
exception, but we may panic before that.  Move the check; this is
consistent with arm64 and serves to ensure that we don't call vm_fault()
etc. from a context where that's not permitted.

Also fix a related bug: don't enable interrupts if they were disabled in
the context where the exception occurred.

Reviewed by:	br
Tested by:	br
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D47688
This commit is contained in:
Mark Johnston 2024-12-10 15:07:28 +00:00
parent e02029e6f4
commit c226f19351
1 changed files with 7 additions and 6 deletions
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13
sys/riscv/riscv/trap.c
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@ -227,11 +227,6 @@ page_fault_handler(struct trapframe *frame, int usermode)
pcb = td->td_pcb;
stval = frame->tf_stval;
if (td->td_critnest != 0 || td->td_intr_nesting_level != 0 ||
WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
"Kernel page fault") != 0)
goto fatal;
if (usermode) {
if (!VIRT_IS_VALID(stval)) {
call_trapsignal(td, SIGSEGV, SEGV_MAPERR, (void *)stval,
@ -244,7 +239,8 @@ page_fault_handler(struct trapframe *frame, int usermode)
* Enable interrupts for the duration of the page fault. For
* user faults this was done already in do_trap_user().
*/
intr_enable();
if ((frame->tf_sstatus & SSTATUS_SIE) != 0)
intr_enable();
if (stval >= VM_MIN_KERNEL_ADDRESS) {
map = kernel_map;
@ -268,6 +264,11 @@ page_fault_handler(struct trapframe *frame, int usermode)
if (VIRT_IS_VALID(va) && pmap_fault(map->pmap, va, ftype))
goto done;
if (td->td_critnest != 0 || td->td_intr_nesting_level != 0 ||
WITNESS_CHECK(WARN_SLEEPOK | WARN_GIANTOK, NULL,
"Kernel page fault") != 0)
goto fatal;
error = vm_fault_trap(map, va, ftype, VM_FAULT_NORMAL, &sig, &ucode);
if (error != KERN_SUCCESS) {
if (usermode) {