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Subject[PATCH v2 14/14] x86/fault, x86/efi: Fix and rename efi_recover_from_page_fault()
Date
efi_recover_from_page_fault() doesn't recover -- it does a special EFI
mini-oops. Rename it to make it clear that it crashes.

While renaming it, I noticed a blatant bug: a page fault oops in a
different thread happening concurrently with an EFI runtime service call
would be misinterpreted as an EFI page fault. Fix that.

This isn't quite exact. We could do better by using a special CS for
calls into EFI.

Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/include/asm/efi.h | 2 +-
arch/x86/mm/fault.c | 11 ++++++-----
arch/x86/platform/efi/quirks.c | 16 ++++++++++++----
3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index c98f78330b09..4b7706ddd8b6 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -150,7 +150,7 @@ extern void __init efi_apply_memmap_quirks(void);
extern int __init efi_reuse_config(u64 tables, int nr_tables);
extern void efi_delete_dummy_variable(void);
extern void efi_switch_mm(struct mm_struct *mm);
-extern void efi_recover_from_page_fault(unsigned long phys_addr);
+extern void efi_crash_gracefully_on_page_fault(unsigned long phys_addr);
extern void efi_free_boot_services(void);

/* kexec external ABI */
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index eed217d4a877..dfdd56d9c020 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -16,7 +16,7 @@
#include <linux/prefetch.h> /* prefetchw */
#include <linux/context_tracking.h> /* exception_enter(), ... */
#include <linux/uaccess.h> /* faulthandler_disabled() */
-#include <linux/efi.h> /* efi_recover_from_page_fault()*/
+#include <linux/efi.h> /* efi_crash_gracefully_on_page_fault()*/
#include <linux/mm_types.h>

#include <asm/cpufeature.h> /* boot_cpu_has, ... */
@@ -25,7 +25,7 @@
#include <asm/vsyscall.h> /* emulate_vsyscall */
#include <asm/vm86.h> /* struct vm86 */
#include <asm/mmu_context.h> /* vma_pkey() */
-#include <asm/efi.h> /* efi_recover_from_page_fault()*/
+#include <asm/efi.h> /* efi_crash_gracefully_on_page_fault()*/
#include <asm/desc.h> /* store_idt(), ... */
#include <asm/cpu_entry_area.h> /* exception stack */
#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
@@ -700,11 +700,12 @@ page_fault_oops(struct pt_regs *regs, unsigned long error_code,
#endif

/*
- * Buggy firmware could access regions which might page fault, try to
- * recover from such faults.
+ * Buggy firmware could access regions which might page fault. If
+ * this happens, EFI has a special OOPS path that will try to
+ * avoid hanging the system.
*/
if (IS_ENABLED(CONFIG_EFI))
- efi_recover_from_page_fault(address);
+ efi_crash_gracefully_on_page_fault(address);

oops:
/*
diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
index 5a40fe411ebd..0463ef9cddd6 100644
--- a/arch/x86/platform/efi/quirks.c
+++ b/arch/x86/platform/efi/quirks.c
@@ -687,15 +687,25 @@ int efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
* @return: Returns, if the page fault is not handled. This function
* will never return if the page fault is handled successfully.
*/
-void efi_recover_from_page_fault(unsigned long phys_addr)
+void efi_crash_gracefully_on_page_fault(unsigned long phys_addr)
{
if (!IS_ENABLED(CONFIG_X86_64))
return;

+ /*
+ * If we are in an interrupt nested inside an EFI runtime service,
+ * then this is a regular OOPS, not an EFI failure.
+ */
+ if (in_interrupt() || in_nmi() || in_softirq())
+ return;
+
/*
* Make sure that an efi runtime service caused the page fault.
+ * READ_ONCE() because we might be OOPSing in a different thread,
+ * and we don't want to trip KTSAN while trying to OOPS.
*/
- if (efi_rts_work.efi_rts_id == EFI_NONE)
+ if (READ_ONCE(efi_rts_work.efi_rts_id) == EFI_NONE ||
+ current_work() != &efi_rts_work.work)
return;

/*
@@ -747,6 +757,4 @@ void efi_recover_from_page_fault(unsigned long phys_addr)
set_current_state(TASK_IDLE);
schedule();
}
-
- return;
}
--
2.29.2
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