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charset="us-ascii" Content-ID: <4A01E3D3C7A22B448988692E65429AA9@namprd15.prod.outlook.com> MIME-Version: 1.0 X-OriginatorOrg: fb.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SA1PR15MB5109.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 4d80f0c1-fdd1-4edc-ba17-08da389bdaab X-MS-Exchange-CrossTenant-originalarrivaltime: 18 May 2022 06:58:46.5963 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: BK1ZPzwWMpMCqAGew7oOdr1EgxA/pYHO9u/j0W7Acg+dVl+bX8SF0DfnnhUsP6YLY3K+zkKyoNDoCClPSJr4UA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR15MB3008 X-Proofpoint-GUID: xZmYKC1uVNn2CvrkaTBQ51Mgju59PMHh X-Proofpoint-ORIG-GUID: xZmYKC1uVNn2CvrkaTBQ51Mgju59PMHh X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-18_02,2022-05-17_02,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, > On May 15, 2022, at 10:40 PM, Song Liu wrote: > > Introduce a memset like API for text_poke. This will be used to fill the > unused RX memory with illegal instructions. > > Suggested-by: Peter Zijlstra > Signed-off-by: Song Liu Could you please share your comments on this? Thanks, Song > --- > arch/x86/include/asm/text-patching.h | 1 + > arch/x86/kernel/alternative.c | 70 ++++++++++++++++++++++++---- > 2 files changed, 61 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h > index d20ab0921480..1cc15528ce29 100644 > --- a/arch/x86/include/asm/text-patching.h > +++ b/arch/x86/include/asm/text-patching.h > @@ -45,6 +45,7 @@ extern void *text_poke(void *addr, const void *opcode, size_t len); > extern void text_poke_sync(void); > extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len); > extern void *text_poke_copy(void *addr, const void *opcode, size_t len); > +extern void *text_poke_set(void *addr, int c, size_t len); > extern int poke_int3_handler(struct pt_regs *regs); > extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate); > > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index d374cb3cf024..732814065389 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -994,7 +994,21 @@ static inline void unuse_temporary_mm(temp_mm_state_t prev_state) > __ro_after_init struct mm_struct *poking_mm; > __ro_after_init unsigned long poking_addr; > > -static void *__text_poke(void *addr, const void *opcode, size_t len) > +static void text_poke_memcpy(void *dst, const void *src, size_t len) > +{ > + memcpy(dst, src, len); > +} > + > +static void text_poke_memset(void *dst, const void *src, size_t len) > +{ > + int c = *(int *)src; > + > + memset(dst, c, len); > +} > + > +typedef void text_poke_f(void *dst, const void *src, size_t len); > + > +static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len) > { > bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE; > struct page *pages[2] = {NULL}; > @@ -1059,7 +1073,7 @@ static void *__text_poke(void *addr, const void *opcode, size_t len) > prev = use_temporary_mm(poking_mm); > > kasan_disable_current(); > - memcpy((u8 *)poking_addr + offset_in_page(addr), opcode, len); > + func((u8 *)poking_addr + offset_in_page(addr), src, len); > kasan_enable_current(); > > /* > @@ -1087,11 +1101,13 @@ static void *__text_poke(void *addr, const void *opcode, size_t len) > (cross_page_boundary ? 2 : 1) * PAGE_SIZE, > PAGE_SHIFT, false); > > - /* > - * If the text does not match what we just wrote then something is > - * fundamentally screwy; there's nothing we can really do about that. > - */ > - BUG_ON(memcmp(addr, opcode, len)); > + if (func == text_poke_memcpy) { > + /* > + * If the text does not match what we just wrote then something is > + * fundamentally screwy; there's nothing we can really do about that. > + */ > + BUG_ON(memcmp(addr, src, len)); > + } > > local_irq_restore(flags); > pte_unmap_unlock(ptep, ptl); > @@ -1118,7 +1134,7 @@ void *text_poke(void *addr, const void *opcode, size_t len) > { > lockdep_assert_held(&text_mutex); > > - return __text_poke(addr, opcode, len); > + return __text_poke(text_poke_memcpy, addr, opcode, len); > } > > /** > @@ -1137,7 +1153,7 @@ void *text_poke(void *addr, const void *opcode, size_t len) > */ > void *text_poke_kgdb(void *addr, const void *opcode, size_t len) > { > - return __text_poke(addr, opcode, len); > + return __text_poke(text_poke_memcpy, addr, opcode, len); > } > > /** > @@ -1167,7 +1183,41 @@ void *text_poke_copy(void *addr, const void *opcode, size_t len) > > s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched); > > - __text_poke((void *)ptr, opcode + patched, s); > + __text_poke(text_poke_memcpy, (void *)ptr, opcode + patched, s); > + patched += s; > + } > + mutex_unlock(&text_mutex); > + return addr; > +} > + > +/** > + * text_poke_set - memset into (an unused part of) RX memory > + * @addr: address to modify > + * @c: the byte to fill the area with > + * @len: length to copy, could be more than 2x PAGE_SIZE > + * > + * Not safe against concurrent execution; useful for JITs to dump > + * new code blocks into unused regions of RX memory. Can be used in > + * conjunction with synchronize_rcu_tasks() to wait for existing > + * execution to quiesce after having made sure no existing functions > + * pointers are live. > + */ > +void *text_poke_set(void *addr, int c, size_t len) > +{ > + unsigned long start = (unsigned long)addr; > + size_t patched = 0; > + > + if (WARN_ON_ONCE(core_kernel_text(start))) > + return NULL; > + > + mutex_lock(&text_mutex); > + while (patched < len) { > + unsigned long ptr = start + patched; > + size_t s; > + > + s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched); > + > + __text_poke(text_poke_memset, (void *)ptr, (void *)&c, s); > patched += s; > } > mutex_unlock(&text_mutex); > -- > 2.30.2 >