diff options
authorLinus Torvalds <>2020-06-18 12:10:37 -0700
committerLinus Torvalds <>2020-06-18 12:10:37 -0700
commit0c389d89abc28edf70ae847ee2fa55acb267b826 (patch)
parent25f12ae45fc1931a1dce3cc59f9989a9d87834b0 (diff)
maccess: make get_kernel_nofault() check for minimal type compatibility
Now that we've renamed probe_kernel_address() to get_kernel_nofault() and made it look and behave more in line with get_user(), some of the subtle type behavior differences end up being more obvious and possibly dangerous. When you do get_user(val, user_ptr); the type of the access comes from the "user_ptr" part, and the above basically acts as val = *user_ptr; by design (except, of course, for the fact that the actual dereference is done with a user access). Note how in the above case, the type of the end result comes from the pointer argument, and then the value is cast to the type of 'val' as part of the assignment. So the type of the pointer is ultimately the more important type both for the access itself. But 'get_kernel_nofault()' may now _look_ similar, but it behaves very differently. When you do get_kernel_nofault(val, kernel_ptr); it behaves like val = *(typeof(val) *)kernel_ptr; except, of course, for the fact that the actual dereference is done with exception handling so that a faulting access is suppressed and returned as the error code. But note how different the casting behavior of the two superficially similar accesses are: one does the actual access in the size of the type the pointer points to, while the other does the access in the size of the target, and ignores the pointer type entirely. Actually changing get_kernel_nofault() to act like get_user() is almost certainly the right thing to do eventually, but in the meantime this patch adds logit to at least verify that the pointer type is compatible with the type of the result. In many cases, this involves just casting the pointer to 'void *' to make it obvious that the type of the pointer is not the important part. It's not how 'get_user()' acts, but at least the behavioral difference is now obvious and explicit. Cc: Christoph Hellwig <> Signed-off-by: Linus Torvalds <>
7 files changed, 11 insertions, 9 deletions
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 49ce15c3612d..17d5a785df28 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -396,7 +396,7 @@ int is_valid_bugaddr(unsigned long pc)
u32 insn = __opcode_to_mem_arm(BUG_INSTR_VALUE);
- if (get_kernel_nofault(bkpt, (unsigned *)pc))
+ if (get_kernel_nofault(bkpt, (void *)pc))
return 0;
return bkpt == insn;
diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
index ad4fc06e5f4b..3a033d2008b3 100644
--- a/arch/ia64/include/asm/sections.h
+++ b/arch/ia64/include/asm/sections.h
@@ -35,7 +35,7 @@ static inline void *dereference_function_descriptor(void *ptr)
struct fdesc *desc = ptr;
void *p;
- if (!get_kernel_nofault(p, &desc->ip))
+ if (!get_kernel_nofault(p, (void *)&desc->ip))
ptr = p;
return ptr;
diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index 6c435dbccca0..b7abb12edd3a 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -293,7 +293,7 @@ void *dereference_function_descriptor(void *ptr)
Elf64_Fdesc *desc = ptr;
void *p;
- if (!get_kernel_nofault(p, &desc->addr))
+ if (!get_kernel_nofault(p, (void *)&desc->addr))
ptr = p;
return ptr;
diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
index bd311616fca8..324d7b298ec3 100644
--- a/arch/powerpc/include/asm/sections.h
+++ b/arch/powerpc/include/asm/sections.h
@@ -85,7 +85,7 @@ static inline void *dereference_function_descriptor(void *ptr)
struct ppc64_opd_entry *desc = ptr;
void *p;
- if (!get_kernel_nofault(p, &desc->funcaddr))
+ if (!get_kernel_nofault(p, (void *)&desc->funcaddr))
ptr = p;
return ptr;
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index e14a1862a3ca..409080208a6c 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -421,7 +421,7 @@ int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
unsigned int instr;
struct ppc_inst *addr = (struct ppc_inst *)bpt->bpt_addr;
- err = get_kernel_nofault(instr, addr);
+ err = get_kernel_nofault(instr, (unsigned *) addr);
if (err)
return err;
diff --git a/arch/x86/kernel/probe_roms.c b/arch/x86/kernel/probe_roms.c
index 65b0dd2bf25c..9e1def3744f2 100644
--- a/arch/x86/kernel/probe_roms.c
+++ b/arch/x86/kernel/probe_roms.c
@@ -94,7 +94,7 @@ static bool match_id(struct pci_dev *pdev, unsigned short vendor, unsigned short
static bool probe_list(struct pci_dev *pdev, unsigned short vendor,
- const unsigned char *rom_list)
+ const void *rom_list)
unsigned short device;
@@ -119,7 +119,7 @@ static struct resource *find_oprom(struct pci_dev *pdev)
for (i = 0; i < ARRAY_SIZE(adapter_rom_resources); i++) {
struct resource *res = &adapter_rom_resources[i];
unsigned short offset, vendor, device, list, rev;
- const unsigned char *rom;
+ const void *rom;
if (res->end == 0)
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index a508a3c08879..0a76ddc07d59 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -324,8 +324,10 @@ long strnlen_user_nofault(const void __user *unsafe_addr, long count);
* Returns 0 on success, or -EFAULT.
-#define get_kernel_nofault(val, ptr) \
- copy_from_kernel_nofault(&(val), (ptr), sizeof(val))
+#define get_kernel_nofault(val, ptr) ({ \
+ const typeof(val) *__gk_ptr = (ptr); \
+ copy_from_kernel_nofault(&(val), __gk_ptr, sizeof(val));\
#ifndef user_access_begin
#define user_access_begin(ptr,len) access_ok(ptr, len)