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Message-ID: <20221104212433.1339826-1-seanjc@google.com>
Date: Fri, 4 Nov 2022 21:24:33 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org
Cc: "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
syzbot+ffb4f000dc2872c93f62@...kaller.appspotmail.com,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Alexander Potapenko <glider@...gle.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Vincenzo Frascino <vincenzo.frascino@....com>,
kasan-dev@...glegroups.com, Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH] x86/mm: Populate KASAN shadow for per-CPU GDT mapping in CPU
entry area
Bounce through cea_map_percpu_pages() when setting protections for the
per-CPU GDT mapping so that KASAN populates a shadow for said mapping.
Failure to populate the shadow will result in a not-present #PF during
KASAN validation if the kernel performs a software lookup into the GDT.
The bug is most easily reproduced by doing a sigreturn with a garbage
CS in the sigcontext, e.g.
int main(void)
{
struct sigcontext regs;
syscall(__NR_mmap, 0x1ffff000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
syscall(__NR_mmap, 0x20000000ul, 0x1000000ul, 7ul, 0x32ul, -1, 0ul);
syscall(__NR_mmap, 0x21000000ul, 0x1000ul, 0ul, 0x32ul, -1, 0ul);
memset(®s, 0, sizeof(regs));
regs.cs = 0x1d0;
syscall(__NR_rt_sigreturn);
return 0;
}
to coerce the kernel into doing a GDT lookup to compute CS.base when
reading the instruction bytes on the subsequent #GP to determine whether
or not the #GP is something the kernel should handle, e.g. to fixup UMIP
violations or to emulate CLI/STI for IOPL=3 applications.
BUG: unable to handle page fault for address: fffffbc8379ace00
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 16c03a067 P4D 16c03a067 PUD 15b990067 PMD 15b98f067 PTE 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 3 PID: 851 Comm: r2 Not tainted 6.1.0-rc3-next-20221103+ #432
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:kasan_check_range+0xdf/0x190
Call Trace:
<TASK>
get_desc+0xb0/0x1d0
insn_get_seg_base+0x104/0x270
insn_fetch_from_user+0x66/0x80
fixup_umip_exception+0xb1/0x530
exc_general_protection+0x181/0x210
asm_exc_general_protection+0x22/0x30
RIP: 0003:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0003:0000000000000000 EFLAGS: 00000202
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000000001d0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Fixes: 9fd429c28073 ("x86/kasan: Map shadow for percpu pages on demand")
Reported-by: syzbot+ffb4f000dc2872c93f62@...kaller.appspotmail.com
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Alexander Potapenko <glider@...gle.com>
Cc: Andrey Konovalov <andreyknvl@...il.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Vincenzo Frascino <vincenzo.frascino@....com>
Cc: kasan-dev@...glegroups.com
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/mm/cpu_entry_area.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index dff9001e5e12..4a6440461c10 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -195,7 +195,7 @@ static void __init setup_cpu_entry_area(unsigned int cpu)
pgprot_t tss_prot = PAGE_KERNEL;
#endif
- cea_set_pte(&cea->gdt, get_cpu_gdt_paddr(cpu), gdt_prot);
+ cea_map_percpu_pages(&cea->gdt, get_cpu_gdt_rw(cpu), 1, gdt_prot);
cea_map_percpu_pages(&cea->entry_stack_page,
per_cpu_ptr(&entry_stack_storage, cpu), 1,
base-commit: 81214a573d19ae2fa5b528286ba23cd1cb17feec
--
2.38.1.431.g37b22c650d-goog
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