From: Christophe Leroy christophe.leroy@c-s.fr
commit 6ec20aa2e510b6297906c45f009aa08b2d97269a upstream.
At the moment, bad_kuap_fault() reports a fault only if a bad access to userspace occurred while access to userspace was not granted.
But if a fault occurs for a write outside the allowed userspace segment(s) that have been unlocked, bad_kuap_fault() fails to detect it and the kernel loops forever in do_page_fault().
Fix it by checking that the accessed address is within the allowed range.
Fixes: a68c31fc01ef ("powerpc/32s: Implement Kernel Userspace Access Protection") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Christophe Leroy christophe.leroy@c-s.fr Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/f48244e9485ada0a304ed33ccbb8da271180c80d.157986675... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/include/asm/book3s/32/kup.h | 9 +++++++-- arch/powerpc/include/asm/book3s/64/kup-radix.h | 3 ++- arch/powerpc/include/asm/kup.h | 6 +++++- arch/powerpc/include/asm/nohash/32/kup-8xx.h | 3 ++- arch/powerpc/mm/fault.c | 2 +- 5 files changed, 17 insertions(+), 6 deletions(-)
--- a/arch/powerpc/include/asm/book3s/32/kup.h +++ b/arch/powerpc/include/asm/book3s/32/kup.h @@ -131,12 +131,17 @@ static inline void prevent_user_access(v kuap_update_sr(mfsrin(addr) | SR_KS, addr, end); /* set Ks */ }
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write) +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; + if (!is_write) return false;
- return WARN(!regs->kuap, "Bug: write fault blocked by segment registers !"); + return WARN(address < begin || address >= end, + "Bug: write fault blocked by segment registers !"); }
#endif /* CONFIG_PPC_KUAP */ --- a/arch/powerpc/include/asm/book3s/64/kup-radix.h +++ b/arch/powerpc/include/asm/book3s/64/kup-radix.h @@ -95,7 +95,8 @@ static inline void prevent_user_access(v set_kuap(AMR_KUAP_BLOCKED); }
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write) +static inline bool +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write) { return WARN(mmu_has_feature(MMU_FTR_RADIX_KUAP) && (regs->kuap & (is_write ? AMR_KUAP_BLOCK_WRITE : AMR_KUAP_BLOCK_READ)), --- a/arch/powerpc/include/asm/kup.h +++ b/arch/powerpc/include/asm/kup.h @@ -45,7 +45,11 @@ static inline void allow_user_access(voi unsigned long size) { } static inline void prevent_user_access(void __user *to, const void __user *from, unsigned long size) { } -static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write) { return false; } +static inline bool +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write) +{ + return false; +} #endif /* CONFIG_PPC_KUAP */
static inline void allow_read_from_user(const void __user *from, unsigned long size) --- a/arch/powerpc/include/asm/nohash/32/kup-8xx.h +++ b/arch/powerpc/include/asm/nohash/32/kup-8xx.h @@ -46,7 +46,8 @@ static inline void prevent_user_access(v mtspr(SPRN_MD_AP, MD_APG_KUAP); }
-static inline bool bad_kuap_fault(struct pt_regs *regs, bool is_write) +static inline bool +bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write) { return WARN(!((regs->kuap ^ MD_APG_KUAP) & 0xf0000000), "Bug: fault blocked by AP register !"); --- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -233,7 +233,7 @@ static bool bad_kernel_fault(struct pt_r
// 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, is_write)) + if (bad_kuap_fault(regs, address, is_write)) return true;
// What's left? Kernel fault on user in well defined regions (extable