Messages in this thread | | | Date | Fri, 9 Oct 2020 16:49:07 +0200 | From | Joerg Roedel <> | Subject | Re: [PATCH v2 4/5] x86/boot/64: Explicitly map boot_params and command line |
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On Thu, Oct 08, 2020 at 03:16:22PM -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> > --- > arch/x86/boot/compressed/ident_map_64.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c > index fd957b2625e9..a3613857c532 100644 > --- a/arch/x86/boot/compressed/ident_map_64.c > +++ b/arch/x86/boot/compressed/ident_map_64.c > @@ -21,6 +21,7 @@ > > #include "error.h" > #include "misc.h" > +#include "cmdline.h" > > /* These actually do the work of building the kernel identity maps. */ > #include <linux/pgtable.h> > @@ -109,6 +110,8 @@ static void add_identity_map(unsigned long start, unsigned long end) > /* Locates and clears a region for a new top level page table. */ > void initialize_identity_maps(void) > { > + unsigned long cmdline; > + > /* Exclude the encryption mask from __PHYSICAL_MASK */ > physical_mask &= ~sme_me_mask; > > @@ -149,10 +152,19 @@ void initialize_identity_maps(void) > } > > /* > - * New page-table is set up - map the kernel image and load it > - * into cr3. > + * New page-table is set up - map the kernel image, boot_params and the > + * command line. > + * The uncompressed kernel requires boot_params and the command line to > + * be mapped in the identity mapping. > + * Map them explicitly here in case the compressed kernel does not > + * touch them, or does not touch all the pages covering them. > */ > add_identity_map((unsigned long)_head, (unsigned long)_end); > + add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1)); > + cmdline = get_cmd_line_ptr(); > + add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE); > + > + /* Load the new page-table. */ > write_cr3(top_level_pgt); > }
Reviewed-by: Joerg Roedel <jroedel@suse.de>
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