linux-kernel - [Patch] Do not clear BSS region in x86 stub

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Message-ID: 
 <DS7PR19MB570996A580C6F5D2C9CACCE48BA32@DS7PR19MB5709.namprd19.prod.outlook.com>
Date: Wed, 17 Jul 2024 07:33:08 +0000
From: "Shao, Marshall" <Marshall.Shao@...l.com>
To: "ardb@...nel.org" <ardb@...nel.org>,
        "linux-efi@...r.kernel.org"
	<linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "bp@...en8.de"
	<bp@...en8.de>, "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de"
	<tglx@...utronix.de>
CC: "Mishra, Ashish" <Ashish.Mishra4@...l.com>,
        "Dion, Christopher"
	<Christopher.Dion@...l.com>,
        "Caisse, Joe" <Joe.Caisse@...l.com>,
        "Chia, Jia
 Yuan" <JiaYuan.Chia@...l.com>,
        "Mukundan, Govind" <Govind.Mukundan@...l.com>
Subject: [Patch] Do not clear BSS region in x86 stub

From: Marshall Shao <marshall.shao@...l.com>

Clearing the BSS region may cause the UEFI firmware to malfunction
during boot.

When booting the kernel from an older firmware version that has TPM
enabled and the MemoryOverwriteRequestControl bit set to 1, the
firmware's boot service might encounter an exception if it attempts
to initialize the BSS region within the x86 stub.

To circumvent the firmware exception, it is advisable to enlarge the
BOOT_STACK_SIZE and to perform the initialization of static variables
prior to the decompression of the bzImage.

Signed-off-by: Marshall Shao <marshall.shao@...l.com>
---
 arch/x86/boot/compressed/misc.c         | 8 +++-----
 arch/x86/include/asm/boot.h             | 2 +-
 drivers/firmware/efi/libstub/x86-stub.c | 5 -----
 3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index b70e4a21c15f..bac5a3c55c2c 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -356,11 +356,9 @@ unsigned long decompress_kernel(unsigned char *outbuf, unsigned long virt_addr,
                                void (*error)(char *x))
 {
        unsigned long entry;
-
-       if (!free_mem_ptr) {
-               free_mem_ptr     = (unsigned long)boot_heap;
-               free_mem_end_ptr = (unsigned long)boot_heap + sizeof(boot_heap);
-       }
+       free_mem_ptr     = (unsigned long)boot_heap;
+       free_mem_end_ptr = (unsigned long)boot_heap + sizeof(boot_heap);
+       malloc_ptr = free_mem_ptr;

        if (__decompress(input_data, input_len, NULL, NULL, outbuf, output_len,
                         NULL, error) < 0)
diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
index 3e5b111e619d..312bc87ab027 100644
--- a/arch/x86/include/asm/boot.h
+++ b/arch/x86/include/asm/boot.h
@@ -33,7 +33,7 @@
 #endif

 #ifdef CONFIG_X86_64
-# define BOOT_STACK_SIZE       0x4000
+# define BOOT_STACK_SIZE       0x10000

 /*
  * Used by decompressor's startup_32() to allocate page tables for identity
diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 1983fd3bf392..d92d2ccc709b 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -21,7 +21,6 @@
 #include "efistub.h"
 #include "x86-stub.h"

-extern char _bss[], _ebss[];

 const efi_system_table_t *efi_system_table;
 const efi_dxe_services_table_t *efi_dxe_table;
@@ -476,9 +475,6 @@ efi_status_t __efiapi efi_pe_entry(efi_handle_t handle,
        efi_status_t status;
        char *cmdline_ptr;

-       if (efi_is_native())
-               memset(_bss, 0, _ebss - _bss);
-
        efi_system_table = sys_table_arg;

        /* Check if we were booted by the EFI firmware */
@@ -1000,7 +996,6 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
 void efi_handover_entry(efi_handle_t handle, efi_system_table_t *sys_table_arg,
                        struct boot_params *boot_params)
 {
-       memset(_bss, 0, _ebss - _bss);
        efi_stub_entry(handle, sys_table_arg, boot_params);
 }

--
2.34.1


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