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From:   Evgeniy Baskov <baskov@ispras.ru>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     Evgeniy Baskov <baskov@ispras.ru>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexey Khoroshilov <khoroshilov@ispras.ru>,
        Peter Jones <pjones@redhat.com>, lvc-project@linuxtesting.org,
        x86@kernel.org, linux-efi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: [PATCH v2 09/23] x86/boot: Remove mapping from page fault handler
Date:   Tue, 25 Oct 2022 17:12:47 +0300
Message-Id: <d028f2565984a6bd9a423d669e80fce55b6b83e9.1666705333.git.baskov@ispras.ru>
In-Reply-To: <cover.1666705333.git.baskov@ispras.ru>
References: <cover.1666705333.git.baskov@ispras.ru>
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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.

Signed-off-by: Evgeniy Baskov <baskov@ispras.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