[PATCH v3 20/21] efi: stub: use high allocation for converted command line

Ard Biesheuvel
2016-01-11T13:19:14Z

Before we can move the command line processing before the allocation
of the kernel, which is required for detecting the 'nokaslr' option
which controls that allocation, move the converted command line higher
up in memory, to prevent it from interfering with the kernel itself.

Since x86 needs the address to fit in 32 bits, use UINT_MAX as the upper
bound there. Otherwise, use ULONG_MAX (i.e., no limit)

Cc: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
arch/x86/include/asm/efi.h | 2 ++
drivers/firmware/efi/libstub/efi-stub-helper.c | 14 +++++++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 0010c78c4998..08b1f2f6ea50 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -25,6 +25,8 @@
#define EFI32_LOADER_SIGNATURE "EL32"
#define EFI64_LOADER_SIGNATURE "EL64"

+#define MAX_CMDLINE_ADDRESS UINT_MAX
+
#ifdef CONFIG_X86_32

diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
index f07d4a67fa76..2a7a3015d7e0 100644
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c
+++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
@@ -649,6 +649,10 @@ static u8 *efi_utf16_to_utf8(u8 *dst, const u16 *src, int n)
return dst;
}

+#ifndef MAX_CMDLINE_ADDRESS
+#define MAX_CMDLINE_ADDRESS ULONG_MAX
+#endif
+
/*
* Convert the unicode UEFI command line to ASCII to pass to kernel.
* Size of memory allocated return in *cmd_line_len.
@@ -684,7 +688,15 @@ char *efi_convert_cmdline(efi_system_table_t *sys_table_arg,

options_bytes++; /* NUL termination */

- status = efi_low_alloc(sys_table_arg, options_bytes, 0, &cmdline_addr);
+ /*
+ * Allocate a buffer for the converted command line as high up
+ * in memory as is feasible: x86 needs the command line allocation
+ * to be below 4 GB, but non-x86 architectures may not have any
+ * memory there. So prefer below 4 GB, and allocate anywhere if
+ * that fails.
+ */
+ status = efi_high_alloc(sys_table_arg, options_bytes, 0,
+ &cmdline_addr, MAX_CMDLINE_ADDRESS);
if (status != EFI_SUCCESS)
return NULL;

--
2.5.0