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From:   David Brazdil <dbrazdil@google.com>
To:     kvmarm@lists.cs.columbia.edu
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel-team@android.com, David Brazdil <dbrazdil@google.com>
Subject: [PATCH v4 12/26] kvm: arm64: Add .hyp.data..ro_after_init ELF section
Date:   Wed,  2 Dec 2020 18:41:08 +0000
Message-Id: <20201202184122.26046-13-dbrazdil@google.com>
In-Reply-To: <20201202184122.26046-1-dbrazdil@google.com>
References: <20201202184122.26046-1-dbrazdil@google.com>
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Add rules for renaming the .data..ro_after_init ELF section in KVM nVHE
object files to .hyp.data..ro_after_init, linking it into the kernel
and mapping it in hyp at runtime.

The section is RW to the host, then mapped RO in hyp. The expectation is
that the host populates the variables in the section and they are never
changed by hyp afterwards.

Signed-off-by: David Brazdil <dbrazdil@google.com>
---
 arch/arm64/include/asm/sections.h |  1 +
 arch/arm64/kernel/vmlinux.lds.S   | 10 ++++++++++
 arch/arm64/kvm/arm.c              |  8 ++++++++
 arch/arm64/kvm/hyp/nvhe/hyp.lds.S |  1 +
 4 files changed, 20 insertions(+)

diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h
index 3994169985ef..8ff579361731 100644
--- a/arch/arm64/include/asm/sections.h
+++ b/arch/arm64/include/asm/sections.h
@@ -11,6 +11,7 @@ extern char __alt_instructions[], __alt_instructions_end[];
 extern char __hibernate_exit_text_start[], __hibernate_exit_text_end[];
 extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
 extern char __hyp_text_start[], __hyp_text_end[];
+extern char __hyp_data_ro_after_init_start[], __hyp_data_ro_after_init_end[];
 extern char __idmap_text_start[], __idmap_text_end[];
 extern char __initdata_begin[], __initdata_end[];
 extern char __inittext_begin[], __inittext_end[];
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 1bda604f4c70..4382b5d0645d 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -30,6 +30,13 @@ jiffies = jiffies_64;
 	*(__kvm_ex_table)					\
 	__stop___kvm_ex_table = .;
 
+#define HYPERVISOR_DATA_SECTIONS				\
+	HYP_SECTION_NAME(.data..ro_after_init) : {		\
+		__hyp_data_ro_after_init_start = .;		\
+		*(HYP_SECTION_NAME(.data..ro_after_init))	\
+		__hyp_data_ro_after_init_end = .;		\
+	}
+
 #define HYPERVISOR_PERCPU_SECTION				\
 	. = ALIGN(PAGE_SIZE);					\
 	HYP_SECTION_NAME(.data..percpu) : {			\
@@ -37,6 +44,7 @@ jiffies = jiffies_64;
 	}
 #else /* CONFIG_KVM */
 #define HYPERVISOR_EXTABLE
+#define HYPERVISOR_DATA_SECTIONS
 #define HYPERVISOR_PERCPU_SECTION
 #endif
 
@@ -234,6 +242,8 @@ SECTIONS
 	_sdata = .;
 	RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
 
+	HYPERVISOR_DATA_SECTIONS
+
 	/*
 	 * Data written with the MMU off but read with the MMU on requires
 	 * cache lines to be invalidated, discarding up to a Cache Writeback
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 6c8594378865..40857cbed3d1 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1705,6 +1705,14 @@ static int init_hyp_mode(void)
 		goto out_err;
 	}
 
+	err = create_hyp_mappings(kvm_ksym_ref(__hyp_data_ro_after_init_start),
+				  kvm_ksym_ref(__hyp_data_ro_after_init_end),
+				  PAGE_HYP_RO);
+	if (err) {
+		kvm_err("Cannot map .hyp.data..ro_after_init section\n");
+		goto out_err;
+	}
+
 	err = create_hyp_mappings(kvm_ksym_ref(__start_rodata),
 				  kvm_ksym_ref(__end_rodata), PAGE_HYP_RO);
 	if (err) {
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index bb2d986ff696..5d76ff2ba63e 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -16,4 +16,5 @@ SECTIONS {
 	HYP_SECTION_NAME(.data..percpu) : {
 		PERCPU_INPUT(L1_CACHE_BYTES)
 	}
+	HYP_SECTION(.data..ro_after_init)
 }
-- 
2.29.2.454.gaff20da3a2-goog