kexec: support purgatories with .text.hot sections

Patch series "kexec: Fix kexec_file_load for llvm16 with PGO", v7.

When upreving llvm I realised that kexec stopped working on my test
platform.

The reason seems to be that due to PGO there are multiple .text sections
on the purgatory, and kexec does not supports that.


This patch (of 4):

Clang16 links the purgatory text in two sections when PGO is in use:

  [ 1] .text             PROGBITS         0000000000000000  00000040
       00000000000011a1  0000000000000000  AX       0     0     16
  [ 2] .rela.text        RELA             0000000000000000  00003498
       0000000000000648  0000000000000018   I      24     1     8
  ...
  [17] .text.hot.        PROGBITS         0000000000000000  00003220
       000000000000020b  0000000000000000  AX       0     0     1
  [18] .rela.text.hot.   RELA             0000000000000000  00004428
       0000000000000078  0000000000000018   I      24    17     8

And both of them have their range [sh_addr ... sh_addr+sh_size] on the
area pointed by `e_entry`.

This causes that image->start is calculated twice, once for .text and
another time for .text.hot. The second calculation leaves image->start
in a random location.

Because of this, the system crashes immediately after:

kexec_core: Starting new kernel

Link: https://lkml.kernel.org/r/20230321-kexec_clang16-v7-0-b05c520b7296@chromium.org
Link: https://lkml.kernel.org/r/20230321-kexec_clang16-v7-1-b05c520b7296@chromium.org
Fixes: 93045705 ("kernel/kexec_file.c: split up __kexec_load_puragory")
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Ross Zwisler <zwisler@google.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Philipp Rudo <prudo@redhat.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tom Rix <trix@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

kernel/kexec_file.c

@@ -901,10 +901,22 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 		}
 
 		offset = ALIGN(offset, align);
+
+		/*
+		 * Check if the segment contains the entry point, if so,
+		 * calculate the value of image->start based on it.
+		 * If the compiler has produced more than one .text section
+		 * (Eg: .text.hot), they are generally after the main .text
+		 * section, and they shall not be used to calculate
+		 * image->start. So do not re-calculate image->start if it
+		 * is not set to the initial value, and warn the user so they
+		 * have a chance to fix their purgatory's linker script.
+		 */
 		if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
 		    pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
 		    pi->ehdr->e_entry < (sechdrs[i].sh_addr
-					 + sechdrs[i].sh_size)) {
+					 + sechdrs[i].sh_size) &&
+		    !WARN_ON(kbuf->image->start != pi->ehdr->e_entry)) {
 			kbuf->image->start -= sechdrs[i].sh_addr;
 			kbuf->image->start += kbuf->mem + offset;
 		}