From 96e8fc5818686d4a1591bb6907e7fdb64ef29884 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 30 Jun 2022 09:14:39 +0200 Subject: x86/xen: Use clear_bss() for Xen PV guests Instead of clearing the bss area in assembly code, use the clear_bss() function. This requires to pass the start_info address as parameter to xen_start_kernel() in order to avoid the xen_start_info being zeroed again. Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Reviewed-by: Jan Beulich Reviewed-by: Boris Ostrovsky Link: https://lore.kernel.org/r/20220630071441.28576-2-jgross@suse.com --- arch/x86/kernel/head64.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index bd4a34100ed0..e7e233209a8c 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -426,7 +426,7 @@ void __init do_early_exception(struct pt_regs *regs, int trapnr) /* Don't add a printk in there. printk relies on the PDA which is not initialized yet. */ -static void __init clear_bss(void) +void __init clear_bss(void) { memset(__bss_start, 0, (unsigned long) __bss_stop - (unsigned long) __bss_start); -- cgit v1.2.3 From 38fa5479b41376dc9d7f57e71c83514285a25ca0 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 30 Jun 2022 09:14:40 +0200 Subject: x86: Clear .brk area at early boot The .brk section has the same properties as .bss: it is an alloc-only section and should be cleared before being used. Not doing so is especially a problem for Xen PV guests, as the hypervisor will validate page tables (check for writable page tables and hypervisor private bits) before accepting them to be used. Make sure .brk is initially zero by letting clear_bss() clear the brk area, too. Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Link: https://lore.kernel.org/r/20220630071441.28576-3-jgross@suse.com --- arch/x86/kernel/head64.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index e7e233209a8c..6a3cfaf6b72a 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -430,6 +430,8 @@ void __init clear_bss(void) { memset(__bss_start, 0, (unsigned long) __bss_stop - (unsigned long) __bss_start); + memset(__brk_base, 0, + (unsigned long) __brk_limit - (unsigned long) __brk_base); } static unsigned long get_cmd_line_ptr(void) -- cgit v1.2.3 From 7e09ac27f43b382f5fe9bb7c7f4c465ece1f8a23 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 30 Jun 2022 09:14:41 +0200 Subject: x86: Fix .brk attribute in linker script Commit in Fixes added the "NOLOAD" attribute to the .brk section as a "failsafe" measure. Unfortunately, this leads to the linker no longer covering the .brk section in a program header, resulting in the kernel loader not knowing that the memory for the .brk section must be reserved. This has led to crashes when loading the kernel as PV dom0 under Xen, but other scenarios could be hit by the same problem (e.g. in case an uncompressed kernel is used and the initrd is placed directly behind it). So drop the "NOLOAD" attribute. This has been verified to correctly cover the .brk section by a program header of the resulting ELF file. Fixes: e32683c6f7d2 ("x86/mm: Fix RESERVE_BRK() for older binutils") Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Reviewed-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20220630071441.28576-4-jgross@suse.com --- arch/x86/kernel/vmlinux.lds.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 81aba718ecd5..9487ce8c13ee 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -385,7 +385,7 @@ SECTIONS __end_of_kernel_reserve = .; . = ALIGN(PAGE_SIZE); - .brk (NOLOAD) : AT(ADDR(.brk) - LOAD_OFFSET) { + .brk : AT(ADDR(.brk) - LOAD_OFFSET) { __brk_base = .; . += 64 * 1024; /* 64k alignment slop space */ *(.bss..brk) /* areas brk users have reserved */ -- cgit v1.2.3