The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 35f1c89b0cce247bf0213df243ed902989b1dcda Gitweb: https://git.kernel.org/tip/35f1c89b0cce247bf0213df243ed902989b1dcda Author: Andy Lutomirski luto@kernel.org AuthorDate: Tue, 09 Feb 2021 18:33:33 -08:00 Committer: Borislav Petkov bp@suse.de CommitterDate: Wed, 10 Feb 2021 13:11:41 +01:00
x86/fault: Fix AMD erratum #91 errata fixup for user code
The recent rework of probe_kernel_address() and its conversion to get_kernel_nofault() inadvertently broke is_prefetch(). Before this change, probe_kernel_address() was used as a sloppy "read user or kernel memory" helper, but it doesn't do that any more. The new get_kernel_nofault() reads *kernel* memory only, which completely broke is_prefetch() for user access.
Adjust the code to the correct accessor based on access mode. The manual address bounds check is no longer necessary, since the accessor helpers (get_user() / get_kernel_nofault()) do the right thing all by themselves. As a bonus, by using the correct accessor, the open-coded address bounds check is not needed anymore.
[ bp: Massage commit message. ]
Fixes: eab0c6089b68 ("maccess: unify the probe kernel arch hooks") Signed-off-by: Andy Lutomirski luto@kernel.org Signed-off-by: Borislav Petkov bp@suse.de Reviewed-by: Christoph Hellwig hch@lst.de Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/b91f7f92f3367d2d3a88eec3b09c6aab1b2dc8ef.161292425... --- arch/x86/mm/fault.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index f1f1b5a..441c3e9 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -54,7 +54,7 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr) * 32-bit mode: * * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch. - * Check that here and ignore it. + * Check that here and ignore it. This is AMD erratum #91. * * 64-bit mode: * @@ -83,11 +83,7 @@ check_prefetch_opcode(struct pt_regs *regs, unsigned char *instr, #ifdef CONFIG_X86_64 case 0x40: /* - * In AMD64 long mode 0x40..0x4F are valid REX prefixes - * Need to figure out under what instruction mode the - * instruction was issued. Could check the LDT for lm, - * but for now it's good enough to assume that long - * mode only uses well known segments or kernel. + * In 64-bit mode 0x40..0x4F are valid REX prefixes */ return (!user_mode(regs) || user_64bit_mode(regs)); #endif @@ -127,20 +123,31 @@ is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr) instr = (void *)convert_ip_to_linear(current, regs); max_instr = instr + 15;
- if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE_MAX) - return 0; + /* + * This code has historically always bailed out if IP points to a + * not-present page (e.g. due to a race). No one has ever + * complained about this. + */ + pagefault_disable();
while (instr < max_instr) { unsigned char opcode;
- if (get_kernel_nofault(opcode, instr)) - break; + if (user_mode(regs)) { + if (get_user(opcode, instr)) + break; + } else { + if (get_kernel_nofault(opcode, instr)) + break; + }
instr++;
if (!check_prefetch_opcode(regs, instr, opcode, &prefetch)) break; } + + pagefault_enable(); return prefetch; }