Re: [PATCH v2 01/10] x86/boot: Drop pointless re-implementation of panic()

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 10 Sep 2026, at 15:12, Kiryl Shutsemau wrote:
> On Wed, Sep 09, 2026 at 10:43:23PM +0200, Ard Biesheuvel wrote:
>> 
>> On Wed, 9 Sep 2026, at 21:14, Borislav Petkov wrote:
>> > On Wed, Sep 09, 2026 at 01:55:32PM +0200, Ard Biesheuvel wrote:
>> >> From: Ard Biesheuvel <ardb@kernel.org>
>> >> 
>> >> The decompressor has its own implementation of panic(), which is based
>> >> on the vsnprintf() routine provided by the EFI stub.
>> >> 
>> >> Relying on the EFI stub from code that does not execute in the context
>> >> of the EFI boot services is a bad idea. It is also completely pointless
>> >> in this case, given that the only user of this version of panic() only
>> >> passes a compile time constant string, without any printf conversions.
>> >> 
>> >> So use error() instead of panic() in that case, and drop the panic()
>> >> implementation entirely. This is needed so that the EFI stub's
>> >> vsnprintf() can be modified in a manner that is incompatible with the
>> >> expectations of this caller.
>> >> 
>> >> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
>> >> ---
>> >>  arch/x86/boot/compressed/error.c | 19 -------------------
>> >>  arch/x86/boot/compressed/error.h |  1 -
>> >>  arch/x86/boot/compressed/mem.c   |  2 +-
>> >>  3 files changed, 1 insertion(+), 21 deletions(-)
>> >> 
>> >> diff --git a/arch/x86/boot/compressed/error.c b/arch/x86/boot/compressed/error.c
>> >> index 19a8251de506..ce5ed7d8265e 100644
>> >> --- a/arch/x86/boot/compressed/error.c
>> >> +++ b/arch/x86/boot/compressed/error.c
>> >> @@ -22,22 +22,3 @@ void error(char *m)
>> >>  	while (1)
>> >>  		asm("hlt");
>> >>  }
>> >> -
>> >> -/* EFI libstub  provides vsnprintf() */
>> >> -#ifdef CONFIG_EFI_STUB
>> >> -void panic(const char *fmt, ...)
>> >
>> > So this thing appeared magically in v8 of the TDX unaccepted memory patches
>> > and I don't think we questioned it back then.
>> >
>> > v7's tdx_accept_memory() does error():
>> >
>> > https://lore.kernel.org/all/20220614120231.48165-15-kirill.shutemov@linux.intel.com/
>> >
>> > and v8 started doing panic():
>> >
>> > +void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
>> > +{
>> > +	if (!tdx_enc_status_changed_phys(start, end, true))
>> > +		panic("Accepting memory failed: %#llx-%#llx\n",  start, end);
>> > +}
>> >
>> > https://lore.kernel.org/all/20221207014933.8435-15-kirill.shutemov@linux.intel.com/
>> >
>> > and it switched to it being a vsnprintf() wrapper because it wanted to dump
>> > start and end perhaps.
>> >
>> > But then it ended up dropping the params in v13 and landed upstream with
>> > a single string as an argument.
>> >
>> > Anyway, adding Kiryl/Kirill for comment and leaving in the rest for reference.
>> >
>> 
>> Looking at that v13, it seems the panic() call was added to
>> arch/x86/coco/tdx/tdx-shared.c, which was shared between the kernel proper and
>> the decompressorat the time, and so a panic() implementation was needed in the
>> decompressor too. But that is no longer the case.
>
> Right. I don't mind dropping this panic() from the decompressor. The
> range was already gone since v13 and I never saw the error trigger
> anyway.
>
> Acked-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
>

Thanks. Can this be applied as a fix please? I need it to base efi/next
on it for the next cycle.