linux-hardening - [PATCH v3 09/24] x86/boot: Remove mapping from page fault handler

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Date:   Tue, 22 Nov 2022 14:12:18 +0300
From:   Evgeniy Baskov <baskov@...ras.ru>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Evgeniy Baskov <baskov@...ras.ru>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        Peter Jones <pjones@...hat.com>,
        "Limonciello, Mario" <mario.limonciello@....com>,
        joeyli <jlee@...e.com>, lvc-project@...uxtesting.org,
        x86@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v3 09/24] x86/boot: Remove mapping from page fault handler

After every implicit mapping is removed, this code is no longer needed.

Remove memory mapping from page fault handler to ensure that there are
no hidden invalid memory accesses.

Tested-by: Mario Limonciello <mario.limonciello@....com>
Signed-off-by: Evgeniy Baskov <baskov@...ras.ru>
---
 arch/x86/boot/compressed/ident_map_64.c | 26 ++++++++++---------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index fec795a4ce23..ba5108c58a4e 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -386,27 +386,21 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
 {
 	unsigned long address = native_read_cr2();
 	unsigned long end;
-	bool ghcb_fault;
+	char *msg;
 
-	ghcb_fault = sev_es_check_ghcb_fault(address);
+	if (sev_es_check_ghcb_fault(address))
+		msg = "Page-fault on GHCB page:";
+	else
+		msg = "Unexpected page-fault:";
 
 	address   &= PMD_MASK;
 	end        = address + PMD_SIZE;
 
 	/*
-	 * Check for unexpected error codes. Unexpected are:
-	 *	- Faults on present pages
-	 *	- User faults
-	 *	- Reserved bits set
-	 */
-	if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD))
-		do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
-	else if (ghcb_fault)
-		do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip);
-
-	/*
-	 * Error code is sane - now identity map the 2M region around
-	 * the faulting address.
+	 * Since all memory allocations are made explicit
+	 * now, every page fault at this stage is an
+	 * error and the error handler is there only
+	 * for debug purposes.
 	 */
-	kernel_add_identity_map(address, end, MAP_WRITE);
+	do_pf_error(msg, error_code, address, regs->ip);
 }
-- 
2.37.4