[PATCH v3 1/5] powerpc/book3s64/kuap: Improve error reporting with KUAP
Christophe Leroy
christophe.leroy at csgroup.eu
Tue Dec 8 19:36:58 AEDT 2020
From: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
This partially reverts commit eb232b162446 ("powerpc/book3s64/kuap: Improve
error reporting with KUAP") and update the fault handler to print
[ 55.022514] Kernel attempted to access user page (7e6725b70000) - exploit attempt? (uid: 0)
[ 55.022528] BUG: Unable to handle kernel data access on read at 0x7e6725b70000
[ 55.022533] Faulting instruction address: 0xc000000000e8b9bc
[ 55.022540] Oops: Kernel access of bad area, sig: 11 [#1]
....
when the kernel access userspace address without unlocking AMR.
bad_kuap_fault() is added as part of commit 5e5be3aed230 ("powerpc/mm: Detect
bad KUAP faults") to catch userspace access incorrectly blocked by AMR. Hence
retain the full stack dump there even with hash translation. Also, add a comment
explaining the difference between hash and radix.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
arch/powerpc/include/asm/book3s/32/kup.h | 4 +--
arch/powerpc/include/asm/book3s/64/kup.h | 34 ++++++++++----------
arch/powerpc/include/asm/kup.h | 4 +--
arch/powerpc/include/asm/nohash/32/kup-8xx.h | 4 +--
arch/powerpc/mm/fault.c | 4 +--
5 files changed, 25 insertions(+), 25 deletions(-)
diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index b18cd931e325..32fd4452e960 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -177,8 +177,8 @@ static inline void restore_user_access(unsigned long flags)
allow_user_access(to, to, end - addr, KUAP_READ_WRITE);
}
-static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
- bool is_write, unsigned long error_code)
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{
unsigned long begin = regs->kuap & 0xf0000000;
unsigned long end = regs->kuap << 28;
diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
index f2e6dd78d5e2..7075c92c320c 100644
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -353,29 +353,29 @@ static inline void set_kuap(unsigned long value)
isync();
}
-#define RADIX_KUAP_BLOCK_READ UL(0x4000000000000000)
-#define RADIX_KUAP_BLOCK_WRITE UL(0x8000000000000000)
-
static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
- bool is_write, unsigned long error_code)
+ bool is_write)
{
if (!mmu_has_feature(MMU_FTR_BOOK3S_KUAP))
return false;
-
- if (radix_enabled()) {
- /*
- * Will be a storage protection fault.
- * Only check the details of AMR[0]
- */
- return WARN((regs->kuap & (is_write ? RADIX_KUAP_BLOCK_WRITE : RADIX_KUAP_BLOCK_READ)),
- "Bug: %s fault blocked by AMR!", is_write ? "Write" : "Read");
- }
/*
- * We don't want to WARN here because userspace can setup
- * keys such that a kernel access to user address can cause
- * fault
+ * For radix this will be a storage protection fault (DSISR_PROTFAULT).
+ * For hash this will be a key fault (DSISR_KEYFAULT)
*/
- return !!(error_code & DSISR_KEYFAULT);
+ /*
+ * We do have exception table entry, but accessing the
+ * userspace results in fault. This could be because we
+ * didn't unlock the AMR or access is denied by userspace
+ * using a key value that blocks access. We are only interested
+ * in catching the use case of accessing without unlocking
+ * the AMR. Hence check for BLOCK_WRITE/READ against AMR.
+ */
+ if (is_write) {
+ return WARN(((regs->amr & AMR_KUAP_BLOCK_WRITE) == AMR_KUAP_BLOCK_WRITE),
+ "Bug: Write fault blocked by AMR!");
+ }
+ return WARN(((regs->amr & AMR_KUAP_BLOCK_READ) == AMR_KUAP_BLOCK_READ),
+ "Bug: Read fault blocked by AMR!");
}
static __always_inline void allow_user_access(void __user *to, const void __user *from,
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index f8ec679bd2de..5a9820c54da9 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -62,8 +62,8 @@ void setup_kuap(bool disabled);
#else
static inline void setup_kuap(bool disabled) { }
-static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
- bool is_write, unsigned long error_code)
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{
return false;
}
diff --git a/arch/powerpc/include/asm/nohash/32/kup-8xx.h b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
index 7bdd9e5b63ed..567cdc557402 100644
--- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h
@@ -60,8 +60,8 @@ static inline void restore_user_access(unsigned long flags)
mtspr(SPRN_MD_AP, flags);
}
-static inline bool bad_kuap_fault(struct pt_regs *regs, unsigned long address,
- bool is_write, unsigned long error_code)
+static inline bool
+bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
{
return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xff000000),
"Bug: fault blocked by AP register !");
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index c91621df0c61..b12595102525 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -210,7 +210,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
return true;
}
- if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
+ if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT | DSISR_KEYFAULT)) &&
!search_exception_tables(regs->nip)) {
pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
address,
@@ -227,7 +227,7 @@ static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
// Read/write fault in a valid region (the exception table search passed
// above), but blocked by KUAP is bad, it can never succeed.
- if (bad_kuap_fault(regs, address, is_write, error_code))
+ if (bad_kuap_fault(regs, address, is_write))
return true;
// What's left? Kernel fault on user in well defined regions (extable
--
2.25.0
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