From 1d04ba1796936244a514db320976f65e2605640d Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 25 Apr 2016 21:07:08 +0100 Subject: [PATCH] efi/runtime-wrappers: Detect firmware IRQ flag corruption The UEFI spec allows runtime services to be called with interrupts masked or unmasked, and if a runtime service function needs to mask interrupts, it must restore the mask to its original state before returning (i.e. from the PoV of the OS, this does not change across a call). Firmware should never unmask exceptions, as these may then be taken by the OS unexpectedly. Unfortunately, some firmware has been seen to unmask IRQs (and potentially other maskable exceptions) across runtime services calls, leaving IRQ flags corrupted after returning from a runtime services function call. This may be detected by the IRQ tracing code, but often goes unnoticed, leaving a potentially disastrous bug hidden. This patch detects when the IRQ flags are corrupted by an EFI runtime services call, logging the call and specific corruption to the console. While restoring the expected value of the flags is insufficient to avoid problems, we do so to avoid redundant warnings from elsewhere (e.g. IRQ tracing). The set of bits in flags which we want to check is architecture-specific (e.g. we want to check FIQ on arm64, but not the zero flag on x86), so each arch must provide ARCH_EFI_IRQ_FLAGS_MASK to describe those. In the absence of this mask, the check is a no-op, and we redundantly save the flags twice, but that will be short-lived as subsequent patches will implement this and remove the scaffolding. Signed-off-by: Mark Rutland Signed-off-by: Matt Fleming Cc: Ard Biesheuvel Cc: Borislav Petkov Cc: Catalin Marinas Cc: Leif Lindholm Cc: Peter Zijlstra Cc: Robin Murphy Cc: Russell King Cc: Thomas Gleixner Cc: Will Deacon Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1461614832-17633-37-git-send-email-matt@codeblueprint.co.uk Signed-off-by: Ingo Molnar --- drivers/firmware/efi/runtime-wrappers.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c index b9ece37..89dcdb3 100644 --- a/drivers/firmware/efi/runtime-wrappers.c +++ b/drivers/firmware/efi/runtime-wrappers.c @@ -16,11 +16,36 @@ #include #include +#include #include #include +#include #include /* + * Temporary scaffolding until all users provide ARCH_EFI_IRQ_FLAGS_MASK. + */ +#ifdef ARCH_EFI_IRQ_FLAGS_MASK +static void efi_call_virt_check_flags(unsigned long flags, const char *call) +{ + unsigned long cur_flags, mismatch; + + local_save_flags(cur_flags); + + mismatch = flags ^ cur_flags; + if (!WARN_ON_ONCE(mismatch & ARCH_EFI_IRQ_FLAGS_MASK)) + return; + + add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_NOW_UNRELIABLE); + pr_err_ratelimited(FW_BUG "IRQ flags corrupted (0x%08lx=>0x%08lx) by EFI %s\n", + flags, cur_flags, call); + local_irq_restore(flags); +} +#else /* ARCH_EFI_IRQ_FLAGS_MASK */ +static inline void efi_call_virt_check_flags(unsigned long flags, const char *call) {} +#endif /* ARCH_EFI_IRQ_FLAGS_MASK */ + +/* * Arch code can implement the following three template macros, avoiding * reptition for the void/non-void return cases of {__,}efi_call_virt: * @@ -43,16 +68,22 @@ #define efi_call_virt(f, args...) \ ({ \ efi_status_t __s; \ + unsigned long flags; \ arch_efi_call_virt_setup(); \ + local_save_flags(flags); \ __s = arch_efi_call_virt(f, args); \ + efi_call_virt_check_flags(flags, __stringify(f)); \ arch_efi_call_virt_teardown(); \ __s; \ }) #define __efi_call_virt(f, args...) \ ({ \ + unsigned long flags; \ arch_efi_call_virt_setup(); \ + local_save_flags(flags); \ arch_efi_call_virt(f, args); \ + efi_call_virt_check_flags(flags, __stringify(f)); \ arch_efi_call_virt_teardown(); \ }) -- 2.7.4