linux-kernel - [PATCH V3 2/5] efi: Introduce __efi

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Date:   Tue,  4 Sep 2018 15:12:26 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     ricardo.neri@...el.com, matt@...eblueprint.co.uk,
        Sai Praneeth <sai.praneeth.prakhya@...el.com>,
        Al Stone <astone@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH V3 2/5] efi: Introduce __efi_init attribute

From: Sai Praneeth <sai.praneeth.prakhya@...el.com>

Buggy firmware could illegally access some efi regions even after the
kernel has assumed control of the platform. When
"CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS" is enabled, the efi page fault
handler will detect and recover from these illegal accesses.
efi_md_typeattr_format() and memory_type_name are used by the efi page
fault handler to print information about memory descriptor that was
illegally accessed. As the page fault handler is present during/after
kernel boot it doesn't have an __init attribute, but
efi_md_typeattr_format() has it and thus during kernel build, "WARNING:
modpost: Found * section mismatch(es)" build warning is observed. To fix
it, remove __init attribute for efi_md_typeattr_format().

In order to not keep efi_md_typeattr_format() and memory_type_name
needlessly when "CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS" is not selected, add
a new __efi_init attribute whose value changes based on whether the
config option is selected or not.

Suggested-by: Matt Fleming <matt@...eblueprint.co.uk>
Based-on-code-from: Ricardo Neri <ricardo.neri@...el.com>
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc: Al Stone <astone@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Bhupesh Sharma <bhsharma@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 drivers/firmware/efi/efi.c |  4 ++--
 include/linux/efi.h        | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index d8a33a781a57..16571429b19c 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -768,7 +768,7 @@ int __init efi_get_fdt_params(struct efi_fdt_params *params)
 }
 #endif /* CONFIG_EFI_PARAMS_FROM_FDT */
 
-static __initdata char memory_type_name[][20] = {
+static __efi_initdata char memory_type_name[][20] = {
 	"Reserved",
 	"Loader Code",
 	"Loader Data",
@@ -786,7 +786,7 @@ static __initdata char memory_type_name[][20] = {
 	"Persistent Memory",
 };
 
-char * __init efi_md_typeattr_format(char *buf, size_t size,
+char * __efi_init efi_md_typeattr_format(char *buf, size_t size,
 				     const efi_memory_desc_t *md)
 {
 	char *pos;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 855992b15269..6a07e3166fd1 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1107,10 +1107,22 @@ extern int efi_memattr_apply_permissions(struct mm_struct *mm,
 	for_each_efi_memory_desc_in_map(&efi.memmap, md)
 
 /*
+ * __efi_init - if CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS is enabled, remove __init
+ *		modifier.
+ */
+#ifdef CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS
+#define __efi_init
+#define __efi_initdata
+#else
+#define __efi_init __init
+#define __efi_initdata __initdata
+#endif
+
+/*
  * Format an EFI memory descriptor's type and attributes to a user-provided
  * character buffer, as per snprintf(), and return the buffer.
  */
-char * __init efi_md_typeattr_format(char *buf, size_t size,
+char * __efi_init efi_md_typeattr_format(char *buf, size_t size,
 				     const efi_memory_desc_t *md);
 
 /**
-- 
2.7.4