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powerpc/book3s64/kuap: Improve error reporting with KUAP

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This partially reverts commit eb232b1624 ("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 5e5be3aed2 ("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@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201208031539.84878-1-aneesh.kumar@linux.ibm.com
This commit is contained in:
Aneesh Kumar K.V 2020-12-08 08:45:39 +05:30 committed by Michael Ellerman
parent 250ad7a45b
commit 475c8749d9
5 changed files with 25 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/powerpc/include/asm/book3s/32/kup.h
View File

@ -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;

34
arch/powerpc/include/asm/book3s/64/kup.h
View File

@ -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,

4
arch/powerpc/include/asm/kup.h
View File

@ -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;
}

4
arch/powerpc/include/asm/nohash/32/kup-8xx.h
View File

@ -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 !");

4
arch/powerpc/mm/fault.c
View File

@ -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