Commit 81256a50 authored by Kiryl Shutsemau's avatar Kiryl Shutsemau Committed by Ingo Molnar
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x86/mm: Make memremap(MEMREMAP_WB) map memory as encrypted by default 



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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarIngo 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
parent a9ebcb88

arch/x86/include/asm/io.h

+3 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/mm/ioremap.c

+8 −0
Original line number Diff line number Diff line
@@ -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