When upreving llvm I realised that kexec stopped working on my test platform. This patch fixes it.
Signed-off-by: Ricardo Ribalda ribalda@chromium.org --- Changes in v5: - Add warning when multiple text sections are found. Thanks Simon! - Add Fixes tag. - Link to v4: https://lore.kernel.org/r/20230321-kexec_clang16-v4-0-1340518f98e9@chromium....
Changes in v4: - Add Cc: stable - Add linker script for x86 - Add a warning when the kernel image has overlapping sections. - Link to v3: https://lore.kernel.org/r/20230321-kexec_clang16-v3-0-5f016c8d0e87@chromium....
Changes in v3: - Fix initial value. Thanks Ross! - Link to v2: https://lore.kernel.org/r/20230321-kexec_clang16-v2-0-d10e5d517869@chromium....
Changes in v2: - Fix if condition. Thanks Steven!. - Update Philipp email. Thanks Baoquan. - Link to v1: https://lore.kernel.org/r/20230321-kexec_clang16-v1-0-a768fc2c7c4d@chromium....
--- Ricardo Ribalda (2): kexec: Support purgatories with .text.hot sections x86/purgatory: Add linker script
arch/x86/purgatory/.gitignore | 2 ++ arch/x86/purgatory/Makefile | 20 +++++++++---- arch/x86/purgatory/kexec-purgatory.S | 2 +- arch/x86/purgatory/purgatory.lds.S | 57 ++++++++++++++++++++++++++++++++++++ kernel/kexec_file.c | 14 ++++++++- 5 files changed, 87 insertions(+), 8 deletions(-) --- base-commit: 17214b70a159c6547df9ae204a6275d983146f6b change-id: 20230321-kexec_clang16-4510c23d129c
Best regards,
Clang16 links the purgatory text in two sections:
[ 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
Cc: stable@vger.kernel.org Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory") Reviewed-by: Ross Zwisler zwisler@google.com Signed-off-by: Ricardo Ribalda ribalda@chromium.org --- kernel/kexec_file.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index f1a0e4e3fb5c..c7a0e51a6d87 100644 --- a/kernel/kexec_file.c +++ b/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; }
On Thu, 30 Mar 2023 11:44:47 +0200 Ricardo Ribalda ribalda@chromium.org wrote:
Clang16 links the purgatory text in two sections:
[ 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
Cc: stable@vger.kernel.org Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory") Reviewed-by: Ross Zwisler zwisler@google.com Signed-off-by: Ricardo Ribalda ribalda@chromium.org
kernel/kexec_file.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index f1a0e4e3fb5c..c7a0e51a6d87 100644 --- a/kernel/kexec_file.c +++ b/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.*/
+ 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;
Reviewed-by: Steven Rostedt (Google) rostedt@goodmis.org
Thanks Ricardo!
-- Steve
Hi Ricardo,
On Thu, 30 Mar 2023 11:44:47 +0200 Ricardo Ribalda ribalda@chromium.org wrote:
Clang16 links the purgatory text in two sections:
[ 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
Cc: stable@vger.kernel.org Fixes: 930457057abe ("kernel/kexec_file.c: split up __kexec_load_puragory") Reviewed-by: Ross Zwisler zwisler@google.com Signed-off-by: Ricardo Ribalda ribalda@chromium.org
kernel/kexec_file.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c index f1a0e4e3fb5c..c7a0e51a6d87 100644 --- a/kernel/kexec_file.c +++ b/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.*/
+ sechdrs[i].sh_size)) {
+ sechdrs[i].sh_size) &&!WARN_ON(kbuf->image->start != pi->ehdr->e_entry)) {
Looks good to me. I'm not sure if it is better to use WARN_ON_ONCE to avoid spamming the log when there are more than two .text sections or when you reload the kernel. But that's only a rare corner case. So no strong opinion from my side. Either way
Reviewed-by: Philipp Rudo prudo@redhat.com
kbuf->image->start -= sechdrs[i].sh_addr; kbuf->image->start += kbuf->mem + offset; }
linux-stable-mirror@lists.linaro.org
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Philipp Rudo -
Ricardo Ribalda -
Steven Rostedt