linux-kernel - [PATCH 2/2] x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

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Message-ID: <20241017155642.1942514-3-kirill.shutemov@linux.intel.com>
Date: Thu, 17 Oct 2024 18:56:42 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...nel.org>
Cc: Albert Ou <aou@...s.berkeley.edu>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrea Parri <parri.andrea@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Daniel Borkmann <daniel@...earbox.net>,
	Eric Chan <ericchancf@...gle.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Kai Huang <kai.huang@...el.com>,
	Kefeng Wang <wangkefeng.wang@...wei.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Palmer Dabbelt <palmer@...osinc.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Russell King <linux@...linux.org.uk>,
	Samuel Holland <samuel.holland@...ive.com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Yuntao Wang <ytcoode@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Ashish Kalra <ashish.kalra@....com>,
	"Maciej W. Rozycki" <macro@...am.me.uk>
Subject: [PATCH 2/2] x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

Currently memremap(MEMREMAP_WB) produces decrypted/shared mapping:

memremap(MEMREMAP_WB)
  arch_memremap_wb()
    ioremap_cache()
      __ioremap_caller(.encrytped = false)

It is a bad default. On TDX guests, access via shared mapping can be
destructive[1].

Kernel already provides a way to request decrypted mapping explicitly
via MEMREMAP_DEC flag.

Make memremap(MEMREMAP_WB) produce encrypted/private mapping by default
unless MEMREMAP_DEC is specified.

It fixes crash on kexec in TDX guests if CONFIG_EISA is enabled.

[1] https://lore.kernel.org/all/20240822095122.736522-1-kirill.shutemov@linux.intel.com

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Ashish Kalra <ashish.kalra@....com>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>
---
 arch/x86/include/asm/io.h | 3 +++
 arch/x86/mm/ioremap.c     | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index 1d60427379c9..1a3a34b40598 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -180,6 +180,9 @@ extern void __iomem *ioremap_prot(resource_size_t offset, unsigned long size, un
 extern void __iomem *ioremap_encrypted(resource_size_t phys_addr, unsigned long size);
 #define ioremap_encrypted ioremap_encrypted
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags);
+#define arch_memremap_wb arch_memremap_wb
+
 /**
  * ioremap     -   map bus memory into CPU space
  * @offset:    bus address of the memory
diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 70b02fc61d93..fc65a81fd777 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -503,6 +503,14 @@ void iounmap(volatile void __iomem *addr)
 }
 EXPORT_SYMBOL(iounmap);
 
+void *arch_memremap_wb(phys_addr_t phys_addr, size_t size, unsigned long flags)
+{
+	if (flags & MEMREMAP_DEC)
+		return ioremap_cache(phys_addr, size);
+
+	return ioremap_encrypted(phys_addr, size);
+}
+
 /*
  * Convert a physical pointer to a virtual kernel pointer for /dev/mem
  * access
-- 
2.45.2