[PATCH] arm[64]/memremap: don't abuse pfn_valid() to ensure presence of linear map

[Mike Rapoport]

From: Mike Rapoport <rppt at linux.ibm.com>

The semantics of pfn_valid() is to check presence of the memory map for a
PFN and not whether a PFN is covered by the linear map. The memory map may
be present for NOMAP memory regions, but they won't be mapped in the linear
mapping.  Accessing such regions via __va() when they are memremap()'ed
will cause a crash.

On v5.4.y the crash happens on qemu-arm with UEFI [1]:

<1>[    0.084476] 8<--- cut here ---
<1>[    0.084595] Unable to handle kernel paging request at virtual address dfb76000
<1>[    0.084938] pgd = (ptrval)
<1>[    0.085038] [dfb76000] *pgd=5f7fe801, *pte=00000000, *ppte=00000000

...

<4>[    0.093923] [<c0ed6ce8>] (memcpy) from [<c16a06f8>] (dmi_setup+0x60/0x418)
<4>[    0.094204] [<c16a06f8>] (dmi_setup) from [<c16a38d4>] (arm_dmi_init+0x8/0x10)
<4>[    0.094408] [<c16a38d4>] (arm_dmi_init) from [<c0302e9c>] (do_one_initcall+0x50/0x228)
<4>[    0.094619] [<c0302e9c>] (do_one_initcall) from [<c16011e4>] (kernel_init_freeable+0x15c/0x1f8)
<4>[    0.094841] [<c16011e4>] (kernel_init_freeable) from [<c0f028cc>] (kernel_init+0x8/0x10c)
<4>[    0.095057] [<c0f028cc>] (kernel_init) from [<c03010e8>] (ret_from_fork+0x14/0x2c)

On kernels v5.10.y and newer the same crash won't reproduce on ARM because
commit b10d6bca8720 ("arch, drivers: replace for_each_membock() with
for_each_mem_range()") changed the way memory regions are registered in the
resource tree, but that merely covers up the problem.

On ARM64 memory resources registered in yet another way and there the
issue of wrong usage of pfn_valid() to ensure availability of the linear
map is also covered.

Implement arch_memremap_can_ram_remap() on ARM and ARM64 to prevent access
to NOMAP regions via the linear mapping in memremap().

Link: https://lore.kernel.org/all/Yl65zxGgFzF1Okac@sirena.org.uk
Reported-by: "kernelci.org bot" <bot at kernelci.org>
Tested-by: Mark Brown <broonie at kernel.org>
Cc: stable at vger.kernel.org	# 5.4+
Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>
---
 arch/arm/include/asm/io.h   | 4 ++++
 arch/arm/mm/ioremap.c       | 9 ++++++++-
 arch/arm64/include/asm/io.h | 4 ++++
 arch/arm64/mm/ioremap.c     | 8 ++++++++
 kernel/iomem.c              | 2 +-
 5 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
index 0c70eb688a00..fbb2eeea7285 100644
--- a/arch/arm/include/asm/io.h
+++ b/arch/arm/include/asm/io.h
@@ -145,6 +145,10 @@ extern void __iomem * (*arch_ioremap_caller)(phys_addr_t, size_t,
 	unsigned int, void *);
 extern void (*arch_iounmap)(volatile void __iomem *);
 
+extern bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
+					unsigned long flags);
+#define arch_memremap_can_ram_remap arch_memremap_can_ram_remap
+
 /*
  * Bad read/write accesses...
  */
diff --git a/arch/arm/mm/ioremap.c b/arch/arm/mm/ioremap.c
index aa08bcb72db9..6eb1ad24544d 100644
--- a/arch/arm/mm/ioremap.c
+++ b/arch/arm/mm/ioremap.c
@@ -43,7 +43,6 @@
 #include <asm/mach/pci.h>
 #include "mm.h"
 
-
 LIST_HEAD(static_vmlist);
 
 static struct static_vm *find_static_vm_paddr(phys_addr_t paddr,
@@ -493,3 +492,11 @@ void __init early_ioremap_init(void)
 {
 	early_ioremap_setup();
 }
+
+bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
+				 unsigned long flags)
+{
+	unsigned long pfn = PHYS_PFN(offset);
+
+	return memblock_is_map_memory(pfn);
+}
diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index 7fd836bea7eb..3995652daf81 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -192,4 +192,8 @@ extern void __iomem *ioremap_cache(phys_addr_t phys_addr, size_t size);
 extern int valid_phys_addr_range(phys_addr_t addr, size_t size);
 extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t size);
 
+extern bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
+					unsigned long flags);
+#define arch_memremap_can_ram_remap arch_memremap_can_ram_remap
+
 #endif	/* __ASM_IO_H */
diff --git a/arch/arm64/mm/ioremap.c b/arch/arm64/mm/ioremap.c
index b7c81dacabf0..b21f91cd830d 100644
--- a/arch/arm64/mm/ioremap.c
+++ b/arch/arm64/mm/ioremap.c
@@ -99,3 +99,11 @@ void __init early_ioremap_init(void)
 {
 	early_ioremap_setup();
 }
+
+bool arch_memremap_can_ram_remap(resource_size_t offset, size_t size,
+				 unsigned long flags)
+{
+	unsigned long pfn = PHYS_PFN(offset);
+
+	return pfn_is_map_memory(pfn);
+}
diff --git a/kernel/iomem.c b/kernel/iomem.c
index 62c92e43aa0d..e85bed24c0a9 100644
--- a/kernel/iomem.c
+++ b/kernel/iomem.c
@@ -33,7 +33,7 @@ static void *try_ram_remap(resource_size_t offset, size_t size,
 	unsigned long pfn = PHYS_PFN(offset);
 
 	/* In the simple case just return the existing linear address */
-	if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)) &&
+	if (!PageHighMem(pfn_to_page(pfn)) &&
 	    arch_memremap_can_ram_remap(offset, size, flags))
 		return __va(offset);
 

base-commit: b2d229d4ddb17db541098b83524d901257e93845
-- 
2.28.0