linux-kernel - [PATCH] efi/x86: Don't blow away existing initrd

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Message-Id: <20200527232602.21596-1-nivedita@alum.mit.edu>
Date:   Wed, 27 May 2020 19:26:02 -0400
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] efi/x86: Don't blow away existing initrd

Commit
  987053a30016 ("efi/x86: Move command-line initrd loading to efi_main")
moved the command-line initrd loading into efi_main, with a check to
ensure that it was attempted only if the EFI stub was booted via
efi_pe_entry rather than the EFI handover entry.

However, in the case where it was booted via handover entry, and thus an
initrd may have already been loaded by the bootloader, it then wrote 0
for the initrd address and size, removing any existing initrd.

Fix this by checking if size is positive before setting the fields in
the bootparams structure.

Fixes: 987053a30016 ("efi/x86: Move command-line initrd loading to efi_main")
Reported-by: Dan Williams <dan.j.williams@...el.com>
Tested-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 drivers/firmware/efi/libstub/x86-stub.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
index 072b7cf40475..ceb8e16c8b75 100644
--- a/drivers/firmware/efi/libstub/x86-stub.c
+++ b/drivers/firmware/efi/libstub/x86-stub.c
@@ -774,10 +774,12 @@ unsigned long efi_main(efi_handle_t handle,
 			efi_err("Failed to load initrd!\n");
 			goto fail;
 		}
-		efi_set_u64_split(addr, &hdr->ramdisk_image,
-				  &boot_params->ext_ramdisk_image);
-		efi_set_u64_split(size, &hdr->ramdisk_size,
-				  &boot_params->ext_ramdisk_size);
+		if (size > 0) {
+			efi_set_u64_split(addr, &hdr->ramdisk_image,
+					  &boot_params->ext_ramdisk_image);
+			efi_set_u64_split(size, &hdr->ramdisk_size,
+					  &boot_params->ext_ramdisk_size);
+		}
 	}
 
 	/*
-- 
2.26.2