This is a note to let you know that I've just added the patch titled x86/fault: Fix AMD erratum #91 errata fixup for user code to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-fault-fix-amd-erratum-91-errata-fixup-for-user-code.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 35f1c89b0cce247bf0213df243ed902989b1dcda Mon Sep 17 00:00:00 2001 From: Andy Lutomirski <luto@xxxxxxxxxx> Date: Tue, 9 Feb 2021 18:33:33 -0800 Subject: x86/fault: Fix AMD erratum #91 errata fixup for user code From: Andy Lutomirski <luto@xxxxxxxxxx> commit 35f1c89b0cce247bf0213df243ed902989b1dcda upstream. 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@xxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/b91f7f92f3367d2d3a88eec3b09c6aab1b2dc8ef.1612924255.git.luto@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/mm/fault.c | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -53,7 +53,7 @@ kmmio_fault(struct pt_regs *regs, unsign * 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: * @@ -82,11 +82,7 @@ check_prefetch_opcode(struct pt_regs *re #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 @@ -126,20 +122,31 @@ is_prefetch(struct pt_regs *regs, unsign 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; } Patches currently in stable-queue which might be from luto@xxxxxxxxxx are queue-5.10/x86-fault-fix-amd-erratum-91-errata-fixup-for-user-code.patch queue-5.10/random-fix-the-rndreseedcrng-ioctl.patch