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x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default

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Currently memremap(MEMREMAP_WB) can produce decrypted/shared mapping:

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

In such cases, the IORES_MAP_ENCRYPTED flag on the memory will determine
if the resulting mapping is encrypted or decrypted.

Creating a decrypted mapping without explicit request from the caller is
risky:

  - It can inadvertently expose the guest's data and compromise the
    guest.

  - Accessing private memory via shared/decrypted mapping on TDX will
    either trigger implicit conversion to shared or #VE (depending on
    VMM implementation).

    Implicit conversion is destructive: subsequent access to the same
    memory via private mapping will trigger a hard-to-debug #VE crash.

The kernel already provides a way to request decrypted mapping
explicitly via the MEMREMAP_DEC flag.

Modify memremap(MEMREMAP_WB) to produce encrypted/private mapping by
default unless MEMREMAP_DEC is specified or if the kernel runs on
a machine with SME enabled.

It fixes the crash due to #VE on kexec in TDX guests if CONFIG_EISA is
enabled.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20250217163822.343400-3-kirill.shutemov@linux.intel.com
This commit is contained in:
Kirill A. Shutemov 2025-02-17 18:38:21 +02:00 • committed by Ingo Molnar
parent a9ebcb8813
commit 81256a50aa
2 changed files with 11 additions and 0 deletions
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3
arch/x86/include/asm/io.h
View file

@ -175,6 +175,9 @@ 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

8
arch/x86/mm/ioremap.c
View file

@ -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) || cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
return (void __force *)ioremap_cache(phys_addr, size);
return (void __force *)ioremap_encrypted(phys_addr, size);
}
/*
* Convert a physical pointer to a virtual kernel pointer for /dev/mem
* access