linux-kernel - [PATCH] x86/kaslr: try process e820 entries if can not get suitable regions from efi

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Date:   Tue, 5 Jan 2021 16:53:46 +0800
From:   Lin Feng <linfeng23@...wei.com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
CC:     <weidong.huang@...wei.com>, <hogan.wang@...wei.com>,
        <wangxinxin.wang@...wei.com>, <linux-kernel@...r.kernel.org>,
        <ebiederm@...ssion.com>, <ardb@...nel.org>,
        Lin Feng <linfeng23@...wei.com>
Subject: [PATCH] x86/kaslr: try process e820 entries if can not get suitable regions from efi

On efi64 x86_64 system, the EFI_CONVENTIONAL_MEMORY regions will not
be mapped when making EFI runtime calls. So kexec-tools can not get
these from /sys/firmware/efi/runtime-map. Then compressed boot os
can not get suitable regions in process_efi_entries and print debug
message as follow:
	Physical KASLR disabled: no suitable memory region!
To enable physical kaslr with kexec, call process_e820_entries when
no suitable regions in efi memmaps.

Signed-off-by: Lin Feng <linfeng23@...wei.com>

---

I find a regular of Kernel code and data placement with kexec. It
seems unsafe. The reason is showed above.

I'm not familiar with efi firmware. I wonder if there are some risks
to get regions according to e820 when there is no suitable region
in efi memmaps.
---
 arch/x86/boot/compressed/kaslr.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index b92fffbe761f..dbd7244b71aa 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -685,6 +685,7 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
 {
 	struct efi_info *e = &boot_params->efi_info;
 	bool efi_mirror_found = false;
+	bool efi_mem_region_found = false;
 	struct mem_vector region;
 	efi_memory_desc_t *md;
 	unsigned long pmap;
@@ -742,12 +743,13 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
 		    !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
 			continue;
 
+		efi_mem_region_found = false;
 		region.start = md->phys_addr;
 		region.size = md->num_pages << EFI_PAGE_SHIFT;
 		if (process_mem_region(&region, minimum, image_size))
 			break;
 	}
-	return true;
+	return efi_mem_region_found;
 }
 #else
 static inline bool
-- 
2.23.0