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Shutemov" , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Peter Zijlstra , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , Alexey Kardashevskiy , Alexander Shishkin Cc: Jonathan Corbet , Sohil Mehta , Ingo Molnar , Pawan Gupta , Daniel Sneddon , Kai Huang , Sandipan Das , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , Rasmus Villemoes , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , Geert Uytterhoeven , Namhyung Kim , Arnaldo Carvalho de Melo , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org, linux-mm@kvack.org References: <20250707080317.3791624-1-kirill.shutemov@linux.intel.com> <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20250707080317.3791624-3-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: ffmjxhhwmfeoisucmehx9pcby71aa46y X-Rspamd-Queue-Id: CFF8B8000F X-HE-Tag: 1752080087-603547 X-HE-Meta: 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 XnRM30qC 3heaEvFFruaHyMvtyeek3adQmeAAsfDVGM9FwUMyEjZZYRIcnxzxCWvHpvCbB/ayf03zf1y8TOGtJ1Ri+XgskirHldbCUG7nIDdj1XkJj21+mf64Vbnn2yM146l3S50EXgB0rtBa0x2xbZlk6uPVE1iIYzS/DkWxu+kcrzBv0/A7HvsL4R/XoMbMB6qGazO+R8re+bnAVvzuK/cQc9fUG9EDhZx1zyrnfSOqjwX0R6ocQM5q6LGXBSaVR1QrbbX+dg9eVxuin3b3Ua2BTXvl5eYjXptCtzktyfgXNVhmeNui3HvbEwnOW71m73A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/7/25 01:03, Kirill A. Shutemov wrote: > From: Sohil Mehta > > For patching, the kernel initializes a temporary mm area in the lower > half of the address range. See commit 4fc19708b165 ("x86/alternatives: > Initialize temporary mm for patching"). > > Disable LASS enforcement during patching to avoid triggering a #GP > fault. > > The objtool warns due to a call to a non-allowed function that exists > outside of the stac/clac guard, or references to any function with a > dynamic function pointer inside the guard. See the Objtool warnings > section #9 in the document tools/objtool/Documentation/objtool.txt. > > Considering that patching is usually small, replace the memcpy() and > memset() functions in the text poking functions with their open coded > versions. > > Signed-off-by: Sohil Mehta > Signed-off-by: Alexander Shishkin > Signed-off-by: Kirill A. Shutemov > --- > arch/x86/include/asm/smap.h | 33 +++++++++++++++++++++++++++++++-- > arch/x86/kernel/alternative.c | 28 ++++++++++++++++++++++++++-- > 2 files changed, 57 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/smap.h b/arch/x86/include/asm/smap.h > index 4f84d421d1cf..d0cc24348641 100644 > --- a/arch/x86/include/asm/smap.h > +++ b/arch/x86/include/asm/smap.h > @@ -23,18 +23,47 @@ > > #else /* __ASSEMBLER__ */ > > +/* > + * The CLAC/STAC instructions toggle the enforcement of X86_FEATURE_SMAP and > + * X86_FEATURE_LASS. > + * > + * SMAP enforcement is based on the _PAGE_BIT_USER bit in the page tables: the > + * kernel is not allowed to touch pages with the bit set unless the AC bit is > + * set. > + * > + * LASS enforcement is based on bit 63 of the virtual address. The kernel is > + * not allowed to touch memory in the lower half of the virtual address space > + * unless the AC bit is set. > + * > + * Use stac()/clac() when accessing userspace (_PAGE_USER) mappings, > + * regardless of location. > + * > + * Use lass_stac()/lass_clac() when accessing kernel mappings (!_PAGE_USER) > + * in the lower half of the address space. > + * > + * Note: a barrier is implicit in alternative(). > + */ > + > static __always_inline void clac(void) > { > - /* Note: a barrier is implicit in alternative() */ > alternative("", "clac", X86_FEATURE_SMAP); > } > > static __always_inline void stac(void) > { > - /* Note: a barrier is implicit in alternative() */ > alternative("", "stac", X86_FEATURE_SMAP); > } > > +static __always_inline void lass_clac(void) > +{ > + alternative("", "clac", X86_FEATURE_LASS); > +} > + > +static __always_inline void lass_stac(void) > +{ > + alternative("", "stac", X86_FEATURE_LASS); > +} Could we please move the comments about lass_*() closer to the LASS functions? > static __always_inline unsigned long smap_save(void) > { > unsigned long flags; > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index ea1d984166cd..992ece0e879a 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -2447,16 +2447,40 @@ void __init_or_module text_poke_early(void *addr, const void *opcode, > __ro_after_init struct mm_struct *text_poke_mm; > __ro_after_init unsigned long text_poke_mm_addr; > > +/* > + * Text poking creates and uses a mapping in the lower half of the > + * address space. Relax LASS enforcement when accessing the poking > + * address. > + */ > + > static void text_poke_memcpy(void *dst, const void *src, size_t len) > { > - memcpy(dst, src, len); > + lass_stac(); > + > + /* > + * Objtool is picky about what occurs within the STAC/CLAC region > + * because this code runs with protection disabled. Objtool typically > + * does not permit function calls in this area. > + * > + * Avoid using memcpy() here. Instead, open code it. > + */ > + asm volatile("rep movsb" > + : "+D" (dst), "+S" (src), "+c" (len) : : "memory"); > + > + lass_clac(); > } This didn't turn out great. At the _very_ least, we could have a: inline_memcpy_i_really_mean_it() with the rep mov. Or even a #define if we were super paranoid the compiler is out to get us. But _actually_ open-coding inline assembly is far too ugly to live. We can also be a bit more compact about the comments: /* * objtool enforces a strict policy of "no function calls within * AC=1 regions". Adhere to the policy by doing a memcpy() that * will never result in a function call. */