4.9-stable review patch. If anyone has any objections, please let me know.
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From: Ard Biesheuvel ard.biesheuvel@linaro.org
(commit b3879a4d3a31ef14265a52e8d941cf4b0f6627ae upstream)
The ARM decompressor is finicky when it comes to uninitialized variables with local linkage, the reason being that it may relocate .text and .bss independently when executing from ROM. This is only possible if all references into .bss from .text are absolute, and this happens to be the case for references emitted under -fpic to symbols with external linkage, and so all .bss references must involve symbols with external linkage.
When building the ARM stub using clang, the initialized local variable __chunk_size is optimized into a zero-initialized flag that indicates whether chunking is in effect or not. This flag is therefore emitted into .bss, which triggers the ARM decompressor's diagnostics, resulting in a failed build.
Under UEFI, we never execute the decompressor from ROM, so the diagnostic makes little sense here. But we can easily work around the issue by making __chunk_size global instead.
However, given that the file I/O chunking that is controlled by the __chunk_size variable is intended to work around known bugs on various x86 implementations of UEFI, we can simply make the chunking an x86 specific feature. This is an improvement by itself, and also removes the need to parse the efi= options in the stub entirely.
Tested-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Reviewed-by: Matt Fleming matt@codeblueprint.co.uk Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1486380166-31868-8-git-send-email-ard.biesheuvel@li... [ Small readability edits. ] Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/firmware/efi/libstub/efi-stub-helper.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-)
--- a/drivers/firmware/efi/libstub/efi-stub-helper.c +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c @@ -356,6 +356,14 @@ efi_status_t efi_parse_options(char *cmd char *str;
/* + * Currently, the only efi= option we look for is 'nochunk', which + * is intended to work around known issues on certain x86 UEFI + * versions. So ignore for now on other architectures. + */ + if (!IS_ENABLED(CONFIG_X86)) + return EFI_SUCCESS; + + /* * If no EFI parameters were specified on the cmdline we've got * nothing to do. */ @@ -528,7 +536,8 @@ efi_status_t handle_cmdline_files(efi_sy size = files[j].size; while (size) { unsigned long chunksize; - if (size > __chunk_size) + + if (IS_ENABLED(CONFIG_X86) && size > __chunk_size) chunksize = __chunk_size; else chunksize = size;