linux-kernel - [PATCH] x86/compressed/64: Add identity mappings for setup

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Date:   Tue, 5 Jul 2022 21:53:15 -0500
From:   Michael Roth <michael.roth@....com>
To:     <x86@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        NOMURA JUNICHI <junichi.nomura@....com>, <kvm@...r.kernel.org>
Subject: [PATCH] x86/compressed/64: Add identity mappings for setup_data entries

The decompressed kernel initially relies on the identity map set up by
the boot/compressed kernel for accessing things like boot_params. With
the recent introduction of SEV-SNP support, the decompressed kernel
also needs to access the setup_data entries pointed to by
boot_params->hdr.setup_data. This can lead to a crash during early boot
due to these entries not currently being included in the initial
identity map.

Fix this by including mappings for the setup_data entries in the
initial identity map.

Fixes:  b190a043c49a ("x86/sev: Add SEV-SNP feature detection/setup")
Reported-by: Jun'ichi Nomura <junichi.nomura@....com>
Signed-off-by: Michael Roth <michael.roth@....com>
---
 arch/x86/boot/compressed/ident_map_64.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index 44c350d627c7..e2249ec93229 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -110,6 +110,7 @@ void kernel_add_identity_map(unsigned long start, unsigned long end)
 void initialize_identity_maps(void *rmode)
 {
 	unsigned long cmdline;
+	struct setup_data *sd;
 
 	/* Exclude the encryption mask from __PHYSICAL_MASK */
 	physical_mask &= ~sme_me_mask;
@@ -163,6 +164,17 @@ void initialize_identity_maps(void *rmode)
 	cmdline = get_cmd_line_ptr();
 	kernel_add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
 
+	/*
+	 * Also map the setup_data entries passed via boot_params in case they
+	 * need to be accessed by uncompressed kernel via the identity mapping.
+	 */
+	sd = (struct setup_data *)boot_params->hdr.setup_data;
+	while (sd) {
+		kernel_add_identity_map((unsigned long)sd,
+					(unsigned long)sd + sizeof(*sd) + sd->len);
+		sd = (struct setup_data *)sd->next;
+	}
+
 	sev_prep_identity_maps(top_level_pgt);
 
 	/* Load the new page-table. */
-- 
2.25.1