From 16132529cee586ee9a058bb33cfbdcb5d884f6b3 Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Thu, 3 Jun 2021 08:41:44 +0000 Subject: powerpc/32s: Rework Kernel Userspace Access Protection On book3s/32, KUAP is provided by toggling Ks bit in segment registers. One segment register addresses 256M of virtual memory. At the time being, KUAP implements a complex logic to apply the unlock/lock on the exact number of segments covering the user range to access, with saving the boundaries of the range of segments in a member of thread struct. But most if not all user accesses are within a single segment. Rework KUAP with a different approach: - Open only one segment, the one corresponding to the starting address of the range to be accessed. - If a second segment is involved, it will generate a page fault. The segment will then be open by the page fault handler. The kuap member of thread struct will now contain: - The start address of the current on going user access, that will be used to know which segment to lock at the end of the user access. - ~0 when no user access is open - ~1 when additionnal segments are opened by a page fault. Then, at lock time - When only one segment is open, close it. - When several segments are open, close all user segments. Almost 100% of the time, only one segment will be involved. In interrupts, inline the function that unlock/lock all segments, because not inlining them implies a lot of register save/restore. With the patch, writing value 128 in userspace in perf_copy_attr() is done with 16 instructions: 3890: 93 82 04 dc stw r28,1244(r2) 3894: 7d 20 e5 26 mfsrin r9,r28 3898: 55 29 00 80 rlwinm r9,r9,0,2,0 389c: 7d 20 e1 e4 mtsrin r9,r28 38a0: 4c 00 01 2c isync 38a4: 39 20 00 80 li r9,128 38a8: 91 3c 00 00 stw r9,0(r28) 38ac: 81 42 04 dc lwz r10,1244(r2) 38b0: 39 00 ff ff li r8,-1 38b4: 91 02 04 dc stw r8,1244(r2) 38b8: 2c 0a ff fe cmpwi r10,-2 38bc: 41 82 00 88 beq 3944 38c0: 7d 20 55 26 mfsrin r9,r10 38c4: 65 29 40 00 oris r9,r9,16384 38c8: 7d 20 51 e4 mtsrin r9,r10 38cc: 4c 00 01 2c isync ... 3944: 48 00 00 01 bl 3944 3944: R_PPC_REL24 kuap_lock_all_ool Before the patch it was 118 instructions. In reality only 42 are executed in most cases, but GCC is not able to see that a properly aligned user access cannot involve more than one segment. 5060: 39 1d 00 04 addi r8,r29,4 5064: 3d 20 b0 00 lis r9,-20480 5068: 7c 08 48 40 cmplw r8,r9 506c: 40 81 00 08 ble 5074 5070: 3d 00 b0 00 lis r8,-20480 5074: 39 28 ff ff addi r9,r8,-1 5078: 57 aa 00 06 rlwinm r10,r29,0,0,3 507c: 55 29 27 3e rlwinm r9,r9,4,28,31 5080: 39 29 00 01 addi r9,r9,1 5084: 7d 29 53 78 or r9,r9,r10 5088: 91 22 04 dc stw r9,1244(r2) 508c: 7d 20 ed 26 mfsrin r9,r29 5090: 55 29 00 80 rlwinm r9,r9,0,2,0 5094: 7c 08 50 40 cmplw r8,r10 5098: 40 81 00 c0 ble 5158 509c: 7d 46 50 f8 not r6,r10 50a0: 7c c6 42 14 add r6,r6,r8 50a4: 54 c6 27 be rlwinm r6,r6,4,30,31 50a8: 7d 20 51 e4 mtsrin r9,r10 50ac: 3c ea 10 00 addis r7,r10,4096 50b0: 39 29 01 11 addi r9,r9,273 50b4: 7f 88 38 40 cmplw cr7,r8,r7 50b8: 55 29 02 06 rlwinm r9,r9,0,8,3 50bc: 40 9d 00 9c ble cr7,5158 50c0: 2f 86 00 00 cmpwi cr7,r6,0 50c4: 41 9e 00 4c beq cr7,5110 50c8: 2f 86 00 01 cmpwi cr7,r6,1 50cc: 41 9e 00 2c beq cr7,50f8 50d0: 2f 86 00 02 cmpwi cr7,r6,2 50d4: 41 9e 00 14 beq cr7,50e8 50d8: 7d 20 39 e4 mtsrin r9,r7 50dc: 39 29 01 11 addi r9,r9,273 50e0: 3c e7 10 00 addis r7,r7,4096 50e4: 55 29 02 06 rlwinm r9,r9,0,8,3 50e8: 7d 20 39 e4 mtsrin r9,r7 50ec: 39 29 01 11 addi r9,r9,273 50f0: 3c e7 10 00 addis r7,r7,4096 50f4: 55 29 02 06 rlwinm r9,r9,0,8,3 50f8: 7d 20 39 e4 mtsrin r9,r7 50fc: 3c e7 10 00 addis r7,r7,4096 5100: 39 29 01 11 addi r9,r9,273 5104: 7f 88 38 40 cmplw cr7,r8,r7 5108: 55 29 02 06 rlwinm r9,r9,0,8,3 510c: 40 9d 00 4c ble cr7,5158 5110: 7d 20 39 e4 mtsrin r9,r7 5114: 39 29 01 11 addi r9,r9,273 5118: 3c c7 10 00 addis r6,r7,4096 511c: 55 29 02 06 rlwinm r9,r9,0,8,3 5120: 7d 20 31 e4 mtsrin r9,r6 5124: 39 29 01 11 addi r9,r9,273 5128: 3c c6 10 00 addis r6,r6,4096 512c: 55 29 02 06 rlwinm r9,r9,0,8,3 5130: 7d 20 31 e4 mtsrin r9,r6 5134: 39 29 01 11 addi r9,r9,273 5138: 3c c7 30 00 addis r6,r7,12288 513c: 55 29 02 06 rlwinm r9,r9,0,8,3 5140: 7d 20 31 e4 mtsrin r9,r6 5144: 3c e7 40 00 addis r7,r7,16384 5148: 39 29 01 11 addi r9,r9,273 514c: 7f 88 38 40 cmplw cr7,r8,r7 5150: 55 29 02 06 rlwinm r9,r9,0,8,3 5154: 41 9d ff bc bgt cr7,5110 5158: 4c 00 01 2c isync 515c: 39 20 00 80 li r9,128 5160: 91 3d 00 00 stw r9,0(r29) 5164: 38 e0 00 00 li r7,0 5168: 90 e2 04 dc stw r7,1244(r2) 516c: 7d 20 ed 26 mfsrin r9,r29 5170: 65 29 40 00 oris r9,r9,16384 5174: 40 81 00 c0 ble 5234 5178: 7d 47 50 f8 not r7,r10 517c: 7c e7 42 14 add r7,r7,r8 5180: 54 e7 27 be rlwinm r7,r7,4,30,31 5184: 7d 20 51 e4 mtsrin r9,r10 5188: 3d 4a 10 00 addis r10,r10,4096 518c: 39 29 01 11 addi r9,r9,273 5190: 7c 08 50 40 cmplw r8,r10 5194: 55 29 02 06 rlwinm r9,r9,0,8,3 5198: 40 81 00 9c ble 5234 519c: 2c 07 00 00 cmpwi r7,0 51a0: 41 82 00 4c beq 51ec 51a4: 2c 07 00 01 cmpwi r7,1 51a8: 41 82 00 2c beq 51d4 51ac: 2c 07 00 02 cmpwi r7,2 51b0: 41 82 00 14 beq 51c4 51b4: 7d 20 51 e4 mtsrin r9,r10 51b8: 39 29 01 11 addi r9,r9,273 51bc: 3d 4a 10 00 addis r10,r10,4096 51c0: 55 29 02 06 rlwinm r9,r9,0,8,3 51c4: 7d 20 51 e4 mtsrin r9,r10 51c8: 39 29 01 11 addi r9,r9,273 51cc: 3d 4a 10 00 addis r10,r10,4096 51d0: 55 29 02 06 rlwinm r9,r9,0,8,3 51d4: 7d 20 51 e4 mtsrin r9,r10 51d8: 3d 4a 10 00 addis r10,r10,4096 51dc: 39 29 01 11 addi r9,r9,273 51e0: 7c 08 50 40 cmplw r8,r10 51e4: 55 29 02 06 rlwinm r9,r9,0,8,3 51e8: 40 81 00 4c ble 5234 51ec: 7d 20 51 e4 mtsrin r9,r10 51f0: 39 29 01 11 addi r9,r9,273 51f4: 3c ea 10 00 addis r7,r10,4096 51f8: 55 29 02 06 rlwinm r9,r9,0,8,3 51fc: 7d 20 39 e4 mtsrin r9,r7 5200: 39 29 01 11 addi r9,r9,273 5204: 3c e7 10 00 addis r7,r7,4096 5208: 55 29 02 06 rlwinm r9,r9,0,8,3 520c: 7d 20 39 e4 mtsrin r9,r7 5210: 39 29 01 11 addi r9,r9,273 5214: 3c ea 30 00 addis r7,r10,12288 5218: 55 29 02 06 rlwinm r9,r9,0,8,3 521c: 7d 20 39 e4 mtsrin r9,r7 5220: 3d 4a 40 00 addis r10,r10,16384 5224: 39 29 01 11 addi r9,r9,273 5228: 7c 08 50 40 cmplw r8,r10 522c: 55 29 02 06 rlwinm r9,r9,0,8,3 5230: 41 81 ff bc bgt 51ec 5234: 4c 00 01 2c isync Signed-off-by: Christophe Leroy [mpe: Export the ool handlers to fix build errors] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/d9121f96a7c4302946839a0771f5d1daeeb6968c.1622708530.git.christophe.leroy@csgroup.eu --- arch/powerpc/include/asm/book3s/32/kup.h | 150 ++++++++++++++++--------------- 1 file changed, 79 insertions(+), 71 deletions(-) (limited to 'arch/powerpc/include/asm/book3s/32/kup.h') diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h index 68fbe28c6d7e..bac7edae64bf 100644 --- a/arch/powerpc/include/asm/book3s/32/kup.h +++ b/arch/powerpc/include/asm/book3s/32/kup.h @@ -42,36 +42,69 @@ static inline void kuep_unlock(void) #include -static inline void kuap_update_sr(u32 sr, u32 addr, u32 end) -{ - addr &= 0xf0000000; /* align addr to start of segment */ - barrier(); /* make sure thread.kuap is updated before playing with SRs */ - for (;;) { - mtsr(sr, addr); - addr += 0x10000000; /* address of next segment */ - if (addr >= end) - break; - sr += 0x111; /* next VSID */ - sr &= 0xf0ffffff; /* clear VSID overflow */ - } +#define KUAP_NONE (~0UL) +#define KUAP_ALL (~1UL) + +static inline void kuap_lock_one(unsigned long addr) +{ + mtsr(mfsr(addr) | SR_KS, addr); + isync(); /* Context sync required after mtsr() */ +} + +static inline void kuap_unlock_one(unsigned long addr) +{ + mtsr(mfsr(addr) & ~SR_KS, addr); + isync(); /* Context sync required after mtsr() */ +} + +static inline void kuap_lock_all(void) +{ + update_user_segments(mfsr(0) | SR_KS); isync(); /* Context sync required after mtsr() */ } +static inline void kuap_unlock_all(void) +{ + update_user_segments(mfsr(0) & ~SR_KS); + isync(); /* Context sync required after mtsr() */ +} + +void kuap_lock_all_ool(void); +void kuap_unlock_all_ool(void); + +static inline void kuap_lock(unsigned long addr, bool ool) +{ + if (likely(addr != KUAP_ALL)) + kuap_lock_one(addr); + else if (!ool) + kuap_lock_all(); + else + kuap_lock_all_ool(); +} + +static inline void kuap_unlock(unsigned long addr, bool ool) +{ + if (likely(addr != KUAP_ALL)) + kuap_unlock_one(addr); + else if (!ool) + kuap_unlock_all(); + else + kuap_unlock_all_ool(); +} + static inline void kuap_save_and_lock(struct pt_regs *regs) { unsigned long kuap = current->thread.kuap; - u32 addr = kuap & 0xf0000000; - u32 end = kuap << 28; if (kuap_is_disabled()) return; regs->kuap = kuap; - if (unlikely(!kuap)) + if (unlikely(kuap == KUAP_NONE)) return; - current->thread.kuap = 0; - kuap_update_sr(mfsr(addr) | SR_KS, addr, end); /* Set Ks */ + current->thread.kuap = KUAP_NONE; + kuap_lock(kuap, false); } static inline void kuap_user_restore(struct pt_regs *regs) @@ -80,18 +113,12 @@ static inline void kuap_user_restore(struct pt_regs *regs) static inline void kuap_kernel_restore(struct pt_regs *regs, unsigned long kuap) { - u32 addr = regs->kuap & 0xf0000000; - u32 end = regs->kuap << 28; - if (kuap_is_disabled()) return; current->thread.kuap = regs->kuap; - if (unlikely(regs->kuap == kuap)) - return; - - kuap_update_sr(mfsr(addr) & ~SR_KS, addr, end); /* Clear Ks */ + kuap_unlock(regs->kuap, false); } static inline unsigned long kuap_get_and_assert_locked(void) @@ -99,9 +126,9 @@ static inline unsigned long kuap_get_and_assert_locked(void) unsigned long kuap = current->thread.kuap; if (kuap_is_disabled()) - return 0; + return KUAP_NONE; - WARN_ON_ONCE(IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && kuap != 0); + WARN_ON_ONCE(IS_ENABLED(CONFIG_PPC_KUAP_DEBUG) && kuap != KUAP_NONE); return kuap; } @@ -114,8 +141,6 @@ static inline void kuap_assert_locked(void) static __always_inline void allow_user_access(void __user *to, const void __user *from, u32 size, unsigned long dir) { - u32 addr, end; - if (kuap_is_disabled()) return; @@ -125,88 +150,71 @@ static __always_inline void allow_user_access(void __user *to, const void __user if (!(dir & KUAP_WRITE)) return; - addr = (__force u32)to; - - if (unlikely(addr >= TASK_SIZE || !size)) - return; - - end = min(addr + size, TASK_SIZE); - - current->thread.kuap = (addr & 0xf0000000) | ((((end - 1) >> 28) + 1) & 0xf); - kuap_update_sr(mfsr(addr) & ~SR_KS, addr, end); /* Clear Ks */ + current->thread.kuap = (__force u32)to; + kuap_unlock_one((__force u32)to); } static __always_inline void prevent_user_access(void __user *to, const void __user *from, u32 size, unsigned long dir) { - u32 addr, end; + u32 kuap = current->thread.kuap; if (kuap_is_disabled()) return; BUILD_BUG_ON(!__builtin_constant_p(dir)); - if (dir & KUAP_CURRENT_WRITE) { - u32 kuap = current->thread.kuap; - - if (unlikely(!kuap)) - return; - - addr = kuap & 0xf0000000; - end = kuap << 28; - } else if (dir & KUAP_WRITE) { - addr = (__force u32)to; - end = min(addr + size, TASK_SIZE); - - if (unlikely(addr >= TASK_SIZE || !size)) - return; - } else { + if (!(dir & KUAP_WRITE)) return; - } - current->thread.kuap = 0; - kuap_update_sr(mfsr(addr) | SR_KS, addr, end); /* set Ks */ + current->thread.kuap = KUAP_NONE; + kuap_lock(kuap, true); } static inline unsigned long prevent_user_access_return(void) { unsigned long flags = current->thread.kuap; - unsigned long addr = flags & 0xf0000000; - unsigned long end = flags << 28; - void __user *to = (__force void __user *)addr; if (kuap_is_disabled()) - return 0; + return KUAP_NONE; - if (flags) - prevent_user_access(to, to, end - addr, KUAP_READ_WRITE); + if (flags != KUAP_NONE) { + current->thread.kuap = KUAP_NONE; + kuap_lock(flags, true); + } return flags; } static inline void restore_user_access(unsigned long flags) { - unsigned long addr = flags & 0xf0000000; - unsigned long end = flags << 28; - void __user *to = (__force void __user *)addr; - if (kuap_is_disabled()) return; - if (flags) - allow_user_access(to, to, end - addr, KUAP_READ_WRITE); + if (flags != KUAP_NONE) { + current->thread.kuap = flags; + kuap_unlock(flags, true); + } } 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; + unsigned long kuap = regs->kuap; if (kuap_is_disabled()) return false; - return is_write && (address < begin || address >= end); + if (!is_write || kuap == KUAP_ALL) + return false; + if (kuap == KUAP_NONE) + return true; + + /* If faulting address doesn't match unlocked segment, unlock all */ + if ((kuap ^ address) & 0xf0000000) + regs->kuap = KUAP_ALL; + + return false; } #endif /* CONFIG_PPC_KUAP */ -- cgit