Messages in this thread | | | From | Arvind Sankar <> | Date | Mon, 19 Oct 2020 13:12:59 -0400 | Subject | Re: [PATCH v3 1/4] x86/boot/64: Explicitly map boot_params and command line |
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On Mon, Oct 19, 2020 at 04:51:15PM +0200, Borislav Petkov wrote: > On Fri, Oct 16, 2020 at 04:04:01PM -0400, Arvind Sankar wrote: > > Commits > > > > ca0e22d4f011 ("x86/boot/compressed/64: Always switch to own page table") > > 8570978ea030 ("x86/boot/compressed/64: Don't pre-map memory in KASLR code") > > > > set up a new page table in the decompressor stub, but without explicit > > mappings for boot_params and the kernel command line, relying on the #PF > > handler instead. > > > > This is fragile, as boot_params and the command line mappings are > > required for the main kernel. If EARLY_PRINTK and RANDOMIZE_BASE are > > disabled, a QEMU/OVMF boot never accesses the command line in the > > decompressor stub, and so it never gets mapped. The main kernel accesses > > it from the identity mapping if AMD_MEM_ENCRYPT is enabled, and will > > crash. > > > > Fix this by adding back the explicit mapping of boot_params and the > > command line. > > > > Note: the changes also removed the explicit mapping of the main kernel, > > with the result that .bss and .brk may not be in the identity mapping, > > but those don't get accessed by the main kernel before it switches to > > its own page tables. > > > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> > > Reviewed-by: Joerg Roedel <jroedel@suse.de> > > --- > > arch/x86/boot/compressed/head_64.S | 3 +++ > > arch/x86/boot/compressed/ident_map_64.c | 24 +++++++++++++++++++++--- > > 2 files changed, 24 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S > > index 1c80f1738fd9..3976b4e92e1b 100644 > > --- a/arch/x86/boot/compressed/head_64.S > > +++ b/arch/x86/boot/compressed/head_64.S > > @@ -544,6 +544,9 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) > > pushq %rsi > > call set_sev_encryption_mask > > call load_stage2_idt > > + /* Pass boot_params to initialize_identity_maps */ > > + popq %rdi > > + pushq %rdi > > Any reason why you're not doing > > movq (%rsp), %rdi > > here instead? >
No real reason. This will disappear anyway in the cleanup patch.
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